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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6788-6800 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoemission from GaAs cathodes with negative electron affinity (NEA) is applied for producing electron beams with very low longitudinal and transverse velocity spread. GaAs transmission-mode cathodes were activated with Cs and either O2 or NF3 in an extremely high vacuum setup (base pressure below 10−12 mbar). Quantum efficiencies of 20%–25% (at 670 nm) and long dark lifetimes (about 1000 h) could be achieved for both types of activation in a reproducible way. Using a method based on the adiabatic transverse expansion of an electron beam in a spatially decreasing magnetic field, the mean transverse energy (MTE) of the photoemitted electrons was measured systematically, recording longitudinal energy distribution curves. Both the MTE and the longitudinal energy spread strongly depend on the value of NEA and the position of the extracted distribution relative to the bulk conduction band minimum. Electrons with energies above the conduction band minimum are thermalized with the lattice temperature of the cathode, while electrons with energies below this level show a non-Maxwellian distribution with enhanced transverse energies. Thus, when extracting all electrons in a current limited emission mode, the MTE increases with the absolute value of NEA and reaches values up to (approximate)100 meV. By cutting off the low energy electrons with an external potential barrier, the longitudinal as well as transverse energy spread of the extracted electron ensemble are reduced. The MTE could be reduced down to about 28 meV at room temperature and to about 14 meV at liquid nitrogen temperature. The behavior of the MTE was found equivalent for (Cs, O) and for (Cs, F) activation layers on the same cathode. Conclusions about energy loss and scattering in the emission of photoelectrons from NEA GaAs cathodes are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2721-2723 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method to map out the energy distribution N(E(parallel),E⊥) of an electron beam as a function of the longitudinal (E(parallel)) and transverse (E⊥) energy has been developed and applied to study the photoemission process from GaAs(Cs, O) at 90 K. The method proceeds by "marking" electrons with fixed longitudinal energy E(parallel)b and a subsequent measurement of the associated differential transverse energy distribution N⊥(E(parallel)b,E⊥), applying an adiabatic magnetic compression technique. The complete energy distribution N(E(parallel),E⊥) of electrons from a GaAs(Cs, O) photocathode obtained by a stepwise variation of E(parallel)b provides details about the transfer of electrons through the GaAs(Cs, O)–vacuum interface and demonstrates that not only electron energy loss, but also elastic electron scattering is of crucial importance in the escape process. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 7000-7011 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational relaxation and isomerization of internally excited deuterated formyl and isoformyl cations has been investigated on the time scale of 2 ms to 12 s using the nearly interaction-free environment of an ion storage ring. De-excitation of the v2 bending modes of DCO+ and DOC+ due to spontaneous radiative transitions was observed as a function of the storage time by measuring their foil-induced Coulomb explosion using three-dimensional coincident fragment imaging. No isomerization of low-lying vibrational levels of DOC+ ions was observed on the time scales considered. By comparing the Coulomb explosion data to molecular bond angle distributions obtained from vibrational wave function calculations, the time evolution of the mean v2 population is deduced for both isomers. The stored DOC+ ions are found to thermalize with the 300 K black-body radiation, while relaxation of the DCO+ bending vibrations was found to require considerably longer times, in agreement with a predicted very small transition moment of the v2=1 level. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Changes of the volatile organic compounds (VOC) emission capacity and composition of different developmental stages of the tropical tree species Hymenaea courbaril were investigated under field conditions at a remote Amazonian rainforest site. The basal emission capacity of isoprene changed considerably over the course of leaf development, from young to mature and to senescent leaves, ultimately spanning a wide range of observed isoprene basal emission capacities from 0.7 to 111.5 µg C g−1 h−1 during the course of the year. By adjusting the standard emission factors for individual days, the diel courses of instantaneous isoprene emission rates could nevertheless adequately be modelled by a current isoprene algorithm. The results demonstrate the inadequacy of using one single standard emission factor to represent the VOC emission capacity of tropical vegetation for an entire seasonal cycle. A strong linear correlation between the isoprene emission capacity and the gross photosynthetic capacity (GPmax) covering all developmental stages and seasons was observed. The present results provide evidence that leaf photosynthetic properties may confer a valuable basis to model the seasonal variation of isoprenoid emission capacity; especially in tropical regions where the environmental conditions vary less than in temperate regions. In addition to induction and variability of isoprene emission during early leaf development, considerable amounts of monoterpenes were emitted in a light-dependent manner exclusively in the period between bud break and leaf maturity. The fundamental change in emission composition during this stage as a consequence of resource availability (supply side control) or as a plant's response to the higher defence demand of young emerging leaves (demand-side control) is discussed. The finding of a temporary emergence of monoterpene emission may be of general interest in understanding both the ecological functions of isoprenoid production and the regulatory processes involved.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Whereas for extra-tropical regions model estimates of the emission of volatile organic compounds (VOC) predict strong responses to the strong annual cycles of foliar biomass, light intensity and temperature, the tropical regions stand out as a dominant source year round, with only little variability mainly due to the annual cycle of foliar biomass of drought-deciduous trees. As part of the Large Scale Biosphere Atmosphere Experiment in Amazônia (LBA-EUSTACH), a remote secondary tropical forest site was visited in the dry-to-wet season transition campaign, and the trace gas exchange of a strong isoprene emitter and a monoterpene emitter are compared to the wet-to-dry season transition investigations reported earlier. Strong seasonal differences of the emission capacity were observed. The standard emission factor for isoprene emission of young mature leaves of Hymenaea courbaril was about twofold in the end of the dry season (111.5 μgC g−1 h−1 or 41.2 nmol m−2 s−1) compared to old mature leaves investigated in the end of the wet season (45.4 μgC g−1 h−1 or 24.9 nmol m−2 s−1). Standardized monoterpene emission rate of Apeiba tibourbou were 2.1 and 3.6 μgC g−1 h−1 (or 0.3 and 0.8 nmol m−2 s-1), respectively. This change in species-specific VOC emission capacity was mirrored by a concurrent change in the ambient mixing ratios. The growth conditions vary less in tropical areas than in temperate regions of the world, and the seasonal differences in emission strength could not be reconciled solely with meteorological data of instantaneous light intensity and temperature. Hence the inadequacy of using a single standard emission factor to represent an entire seasonal cycle is apparent. Among a host of other potential factors, including the leaf developmental stage, water and nutrient status, and abiotic stresses like the oxidative capacity of the ambient air, predominantly the long-term growth temperature may be applied to predict the seasonal variability of the isoprene emission capacity. The dry season isoprene emission rates of H. courbaril measured at the canopy top were also compared to isoprene emissions of the shade-adapted species Sorocea guilleminiana growing in the understory. Despite the difference in VOC emission composition and canopy position, one common algorithm was able to predict the diel emission pattern of all three tree species.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of oral rehabilitation 31 (2004), S. 0 
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Summary  Mismatch occurring during the fabrication of implant-supported dentures may induce stress to the peri-implant bone. The purpose of this study was to investigate the influence of two different alloys and the fabrication method on the marginal accuracy of cast partial dentures. Two laboratory implants were bonded into an aluminium block so that the distance between their longitudinal axes was 21 mm. Frameworks designed for screw-retained partial dentures were cast either with pure titanium (rematitan) or with a CoCr-alloy (remanium CD). Two groups of 10 frameworks were cast in a single piece. The first group was made of pure titanium, and the second group of a CoCr-alloy (remanium CD). A third group of 10 was cast in two pieces and then laser-welded onto a soldering model. This latter group was also made of the CoCr-alloy. All the frameworks were screwed to the original model with defined torque. Using light microscopy, marginal accuracy was determined by measuring vertical gaps at eight defined points around each implant. Titanium frameworks cast in a single piece demonstrated mean vertical gaps of 40 μm (s.d. = 11 μm) compared with 72 μm (s.d. = 40 μm) for CoCr-frameworks. These differences were not significant (U-test, P = 0·124) because of a considerable variation of the values for CoCr-frameworks (minimum: 8 μm and maximum: 216 μm). However, frameworks cast in two pieces and mated with a laser showed significantly better accuracy in comparison with the other experimental groups (mean: 17 μm ± 6; P 〈 0·01). (i) The fit of implant-supported partial dentures cast with pure titanium in a single piece is preferable to that of those made with the CoCr-alloy and (ii) the highest accuracy can be achieved by using a two-piece casting technique combined with laser welding. Manufacturing the framework pieces separately and then welding them together provides the best marginal fit.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1433-0458
    Keywords: Schlüsselwörter ; Digitale Hörgeräte ; Klinische Tests ; Sprachverständnis im Störgeräusch ; Hörflächenaudiometrie ; Frageninventare ; Keywords ; Digital hearing aid ; Clinical trials ; Speech perception in noise ; Loudness scaling ; Self assessment questionnaires
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Abstract The benefit of innovative hearing aid technology can be evaluated in clinical trials. The present study describes the comparison of a new digital hearing aid with an analogue device serving as a reference. The tests were carried out with 15 experienced hearing aid wearers. To prevent the influence of different fitting algorithms such as prescriptive or loudness-based the digital devices were not renewed fitted but their level- and frequency-depending gain was adjusted to that of the reference. Different tests concerning loudness perception (category loudness scaling) speech discrimination in noise (the Göttingen sentence test) and self-assessment of the benefit by questionnaires were performed. All tests yielded slightly better results for the digital hearing aid. The speech audiometric evaluation showed somewhat better discrimination for the test-device. The questionnaires yielded a marked preference for the digital device. Because the study was not blinded influences due to the knowledge of the subjects of testing a new technology generally can occur. On the other hand, the question arises whether present audiometric tests sufficiently consider signal processing of modern hearing systems. Furthermore, one has to take into account that only a few of the features of digital technology such as noise-reduction and feedback-cancellation were considered in this study to allow for a sensible comparison. Because of the large number of possibilities offered by digital technology additional benefit by the hearing aid can be expected.
    Notes: Zusamenfassung Der Nutzen neuer Hörgerätetechnologien kann in klinischen Studien validiert werden. In der vorliegenden Untersuchung wurde ein digitales Hörgerät mit einer analogen Hörgeräteversorgung von 15 erfahrenen Hörgeräteträgern verglichen. Da vermieden werden sollte, dass unterschiedliche Arten der Anpassung wie beispielsweise präskriptiv oder lautheitsbasiert in die Ergebnisse mit eingehen, wurde das zu testende Gerät hinsichtlich seiner pegel- und frequenzabhängigen Verstärkung nicht neu angepaßt, sondern entsprechend der analogen Referenz eingestellt. Es wurden verschiedene Tests durchgeführt, die das Lautheitsempfinden (Hörflächenskalierung), Sprachverstehen im Störgeräusch (Göttinger Satztest) sowie die subjektive Einschätzung des Versorgungserfolgs (Frageninventare) beinhalteten. Insgesamt konnten bei allen Untersuchungen Vorteile für das digitale Gerät festgestellt werden. In den sprachaudiometrischen Tests ergab sich im Mittel eine geringfügig bessere Diskrimination bei der digitalen Versorgung. Die Frageninventare zeigten in Teilbereichen deutlichere Präferenzen für das Testgerät. Da die Studie nicht im Blindversuch durchgeführt werden konnte, sind Einflüsse durch vorgefaßte Meinungen der Versuchspersonen grundsätzlich möglich. Andererseits stellt sich auch die Frage, ob die derzeitigen „objektiven” audiometrischen Testverfahren der Signalverarbeitung moderner Geräte ausreichend Rechnung tragen. Es muß weiterhin berücksichtigt werden, dass hier bewußt nur ein Teil der Verarbeitungsmöglichkeiten, d.h. Störgeräusch- und Rückkopplungsunterdrückung, digitaler Techniken überprüft wurden, um einen sinnvollen Vergleich zu ermöglichen. Da das Potential derartiger moderner Geräte deutlich größer ist, ist weiterer Nutzen für den Patienten zu erwarten.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 7 (2000), S. 103-109 
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Traditionally, depth resolution in diffraction experiments is obtained by inserting pinholes in both the incoming and diffracted beam. For materials science investigations of local strain and texture properties this leads to very slow data-acquisition rates, especially when characterization is performed on the level of the individual grains. To circumvent this problem a conical slit has been manufactured by wire-electrodischarge machining. The conical slit has six 25 µm-thick conically shaped openings matching six of the Debye–Scherrer cones from a face-centred-cubic powder. By combining the slit with a microfocused incoming beam of hard X-rays, an embedded gauge volume is defined. Using a two-dimensional detector, fast and complete information can be obtained regarding the texture and strain properties of the material within this particular gauge volume. The average machining and assemblage errors of the conical slit are found both to be of the order of 5 µm. An algorithm for alignment of the slit is established, and the potential of the technique is illustrated with an example of grain mapping in a 4.5 mm-thick Cu sample.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Der Internist 41 (2000), S. M038 
    ISSN: 1432-1289
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of thermal analysis and calorimetry 61 (2000), S. 37-44 
    ISSN: 1572-8943
    Keywords: enzyme sensor ; IC-calorimeter ; peroxidase ; phenolic compounds ; tyrosinase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This study furnished results on the enzymatic detection of phenolic compounds by means of a miniaturized heat-flow calorimeter (IC-calorimeter). Two enzymes were used: tyrosinase and peroxidase. Additionally to the investigations with the IC-calorimeter, measurements were carried out with a classical reaction calorimeter (LKB 8700) for the very slow reactions with tyrosinase. By way of contrast, the reactions with peroxidase are fast and seem more suitable for sensor application. The detection limit for the investigated phenolic compounds is of the order of 1 mmol l−1 .
    Type of Medium: Electronic Resource
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