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  • 1
    Electronic Resource
    Electronic Resource
    Modeling the spectral response of the quantum well solar cell (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 614-621 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The quantum well solar cell is an alternative to more conventional multiband gap approaches to higher cell efficiency. Preliminary studies have shown that the insertion of a series of quantum wells into the depletion region of a GaAs/AlxGa1−xAs p-i-n solar cell can significantly enhance the cell's short-circuit current. We present here a model for the spectral response of GaAs and AlxGa1−xAs p-n and p-i-n solar cells, with and without quantum wells, based on a standard solution of the minority-carrier equations. Particular emphasis is placed on modeling the absorption coefficient of the AlxGa1−xAs and of the quantum wells. We find that our model can accurately predict the spectral response of a wide variety of cells: both conventional p-n junctions in GaAs and AlxGa1−xAs, and various geometries of quantum well solar cell in AlxGa1−xAs/GaAs (x∼0.3). We discuss the strengths and weaknesses of the model and its underlying assumptions, and conclude by using the model to design p-i-n quantum well solar cells with higher short-circuit current outputs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355275
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  • 2
    Electronic Resource
    Electronic Resource
    Short-circuit current and energy efficiency enhancement in a low-dimensional structure photovoltaic device (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 135-137 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the forward bias behavior of AlGaAs/GaAs p-i-n multiquantum well (MQW) photodiodes. In samples with low background impurity levels in the intrinsic region the high quantum efficiency observed in reverse bias is maintained into forward bias even for carriers photoexcited in the wells. We compare our MQW devices with structures which are identical apart from having AlGaAs intrinsic regions without quantum wells. The short-circuit currents in the MQW structures are much higher than in the control samples though the open-circuit voltages are somewhat smaller. In one case the energy conversion efficiency of the MQW device in white light is 110% higher than the control. We discuss the implications of our results for the development of low-dimensional structure solar cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105553
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  • 3
    Electronic Resource
    Electronic Resource
    Separation of local asymmetry and selective solvation effects using the quadrupole relaxation of the23Na+ and87Rb+ ions in acetonitrile-water mixtures (1983)
    Springer
    Journal of solution chemistry 12 (1983), S. 685-701 
    Details
    ISSN: 1572-8927
    Keywords: Quadrupole relaxation ; 23Na+,87Rb+, and14N NMR ; ion-solvent interaction ; asymmetry effects ; preferential solvation ; acetonitrile-water mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nuclear magnetic relaxation rates of23Na+,87Rb+, and14N in acetonitrile-water mixtures have been measured over the complete mixture range. The interaction of the quadrupole moment of ionic nuclei with electric field gradients is an excellent short ranged probe for the direct neighborhood of ions in solution. Thus the23Na+ and87Rb+ relaxation contains information about dynamics composition and symmetry of the inner solvation sphere in the mixed solvent. It was found that the relaxation rate of both ionic nuclei has an unexpected marked maximum in the acetonitrile (AN) rich region. The14N and2H relaxation rates of the solvent molecules revealed that the maximum could not be explained by dynamic effects. Further experimental results showed that it is caused by local symmetry changes. By measuring 1/T1 of the cationic nuclei in AN-H2O and AN-D2O it was possible for the first time to separate quantitatively asymmetry effects from selective solvation effects. It turned out that both cations are strongly preferentially hydrated. Comparison of the results of two approaches for the evaluation of the D2O-H2O isotope effect led to interesting hints concerning the location of the electric point dipole in acetonitrile molecules having contact with cations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00647381
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  • 4
    Electronic Resource
    Electronic Resource
    The influence of head position and head reorientation on the axis of eye rotation and the vestibular time constant during postrotatory nystagmus (1992)
    Springer
    Experimental brain research 91 (1992), S. 121-128 
    Details
    ISSN: 1432-1106
    Keywords: Vestibuloocular reflex ; Velocity storage ; Active head tilt ; Semicircular canals ; Otolith ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Reorienting the head with respect to gravity during the postrotatory period alters the time course of postrotatory nystagmus (PRN), hastening its decline and thereby reducing the calculated vestibular time constant. One explanation for this phenomenon is that the head reorientation results in a corresponding reorientation of the axis of eye rotation with respect to head coordinates. This possibility was investigated in 10 human subjects whose eye movements were monitored with a three-dimensional magnetic field — search — coil technique using a variety of head reorientation paradigms in a randomized order during PRN following the termination of a 90°/s rotation about earth vertical. Average eye velocities were calculated over two time intervals: from 1 s to 2 s and from 7 s to 8 s after cessation of head rotation. The time constant was estimated as one third of the duration of PRN. For most conditions, a reorientation of the head with respect to gravity 2 s after the rotation had stopped did not significantly alter the direction of the eye velocity vector of PRN with respect to head coordinates. This strongly indicates that, in humans, PRN is mainly stabilized in head coordinates and not in space coordinates, even if the otolith input changes. This finding invalidates the notion that the shortening of PRN due to reorientation of the head could be due to a change of the eye velocity vector towards a direction (torsion), which is not detectable with the eye recording methods (electrooculography) used in earlier studies. The results regarding the vestibular time constant basically confirm earlier findings, showing a strong dependence on static head position, with the time constant being lowest if mainly the vertical canals are stimulated (60° nose up and 90° left ear down). In addition, the time constant was drastically shortened for tilts away from upright. The reduction in vestibular time constant with head reorientation cannot be explained solely on the basis of the dependence of the time constant on static head position. A clear example is provided by head reorientations back towards the upright position, which results in a decrease in the time constant, rather than an increase that would be expected on the basis of static head position.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230020
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  • 5
    Electronic Resource
    Electronic Resource
    Changes in gallbladder motor function during the female cycle — a risk factor leading to gallstone formation? (1982)
    Springer
    Journal of molecular medicine 60 (1982), S. 1357-1362 
    Details
    ISSN: 1432-1440
    Keywords: Gallbladder motor function ; Gallstone formation ; Gallbladder ultrasonography ; Gallbladder contraction ; Gallbladder refilling ; Gallensteinentstehung ; Gallenblasenkontraktion ; Motorische Gallenblasenfunktion ; Gallenblasenfüllung ; Ultraschalldiagnostik
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Bei 8 Frauen mit stabilem Zyklus wurden mittels Sonographie das Gallenblasenvolumen bestimmt und in der Progesteron- sowie der Östrogenphase des Zyklus die Gallenblasenkontraktion nach oraler Reizmahlzeit und die spontane Wiederauffüllung der entleerten Gallenblase quantitativ untersucht. Zur Volumenberechnung wurde die Formel eines Drehellipsoids verwandt, die sich im Modellversuch als hinreichend exakt erwiesen hatte. Die intraindividuellen Vergleichsuntersuchungen zeigten in der Progesteronphase (21. oder 22. Tag) gegenüber der östrogenphase (12. oder 13. Tag) statistisch gesicherte größere Nüchternvolumina, höhere Residualvolumina nach Kontraktion und eine langsamere Gallenblasenentleerung sowie eine verzögerte Wiederauffüllung der entleerten Gallenblase. Dem hormonal modifizierten Kontraktionsverhalten und der unterschiedlich ablaufenden Gallenblasenfüllung könnte im Rahmen der Gallensteinentstehung eine wesentliche Bedeutung zukommen.
    Notes: Summary The gallbladder volume of eight women with stable cycles was determined by sonography. Furthermore, gallbladder contraction — following an orally administered fatty meal and the spontaneous refilling of the empty gallbladder — was quantitatively examined. The formula of a rotation ellipsoid, which has been proven to be adequately accurate in in vitro studies, was used for calculating the gallbladder volume. In the gestagen phase (21st or 22nd day) the intraindividual studies showed greater fasting volumes, higher residual volumes after contraction, slower gallbladder emptying, and retarded refilling of the empty gallbladder as compared to the estrogen phase (12th or 13th day). The hormonally modified contraction behavior and the differing course of gallbladder filling may play a major role in the pathogenesis of gallstone formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01716215
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  • 6
    Electronic Resource
    Electronic Resource
    Potentiometrische und elektrometrische Titrationen (1931)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 86 (1931), S. 258-261 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01359396
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  • 7
    Electronic Resource
    Electronic Resource
    Der Einfluß von Sonographie und Computer-Tomographie auf die operative Behandlung der akuten Pankreatitis (1982)
    Springer
    Langenbeck's archives of surgery 356 (1982), S. 141-149 
    Details
    ISSN: 1435-2451
    Keywords: Acute pancreatitis ; Computed tomography ; Ultrasound ; Operative treatment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Die „stadiengerechte Therapie” der akuten Pankreatitis, die jedem Schweregrad der Erkrankung angemessen ist, besteht neben der konservativen Basistherapie und Intensivmedizin im richtigen Einsatz operativer Maßnahmen. Voraussetzung dafür ist die frühe Diagnose und Beurteilung des Schweregrades der akuten Pankreatitis. Neben klinischen und klinisch-chemischen Befunden und dem Verlauf unter konservativer Therapie ermöglichen die Sonographie und die Computer-Tomographie eine bessere Beurteilung der jeweiligen Verlaufsform. Die für die Klinik der Erkrankung so wichtigen morphologischen Veränderungen der Bauchspeicheldrüse und ihrer Umgebung werden durch diese neuartigen Untersuchungsmethoden transparenter. Wäh rend bei der leichten Pankreatitis die Sonographie als erstes morphologisches Untersuchungsverfahren eingesetzt wird, besteht bei den schweren Verlaufsformen eine klassische Indikation zur Computer-Tomographie. Durch Einsatz von Sonographie und Computer-Tomographie läßt sich die Indikation zur frühzeitigen oder verzögerten Operation der hämorrhagisch-nekrotisierenden Pankreatitis, die bisher nach klinischen Kriterien erfolgte, in den meisten Fällen exakter stellen.
    Notes: Summary Adequate stage-depending therapy of acute pancreatitis includes basic conservative treatment, intensive care measurements, and operative interventions depending on the grade of severity. Prerequisites are early diagnosis and accurate clinical assessment of the stage of severity. Beside clinical and laboratory findings, as well as the development of acute pancreatitis under conservative treatment, sonography and computed tomography allow a better prediction of the underlying morphological changes, thus leading to an exact staging of the patient's individual situation. Sonography is regarded a screening procedure of high accuracy in mild forms of acute pancreatitis. Computed tomography is the method of choice in all severe forms of this disease. The indication for immediate or delayed operative treatment of hemorrhagic necrotising pancreatitis, heretofore depending on clinical findings solely, is supported by these new-invasive diagnostic modalities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01239461
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  • 8
    Electronic Resource
    Electronic Resource
    116. Experimentelle Untersuchungen über eine neuartige gesprühte Kunststoffprothese (1981)
    Springer
    Langenbeck's archives of surgery 355 (1981), S. 517-517 
    Details
    ISSN: 1435-2451
    Keywords: Polyurethane graft ; Microporosity ; Control angiography ; Scanning electronic microscopy ; Polyurethanprothesen ; Mikroporosität ; Kontrollangiographie ; Rasterelektronenmikroskopie
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Die neuen Kunststoffprothesen bestehen aus Polyúrethan, das nach einem speziellen Sprühverfahren verarbeitet wird. Die Prothesen sind längs- und querelastisch sowie mikroporös. In tierexperimentellen Untersuchungen wurden 20mal die terminale Aorta, 24mal die arteria carotis communis und 12mal die arteria femoralis superficialis ersetzt. Die Tiere wurden in regelmäßigen Abst↭den angiographiert. Nach Tötung erfolgten rasterelektronenmikroskopische und histologische Untersuchungen. Von 20 Aortentransplantaten blieben 18 bis zum Zeitpunkt der Tötung, bzw. bis heute offen. In Carotisposition scheinen sich die Transplantate nicht zu bewähren.
    Notes: Summary The new plastic graft consists of polyurethane manufactured in a special spray process. These grafts are elastic both transversally and longitudinally and are microporous. In experiments on animals, the abdominal aorta was substituted 20 times, the common carotid artery 24 times, and the superficial femoral artery 12 times. The animals were regularly subjected to angiographical examinations. After they were killed, they were examined histologically and by means of a scanning electronic microscope. Of the 20 abdominal grafts, 18 have remained open to date. Carotis grafts, however, seemed to fail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01286945
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  • 9
    Electronic Resource
    Electronic Resource
    Supramolecular effects on photochromism - properties of crown ether-modified dihydroindolizinesDedicated to Professor H. G. O. Becker on the occasion of his 70th birthday. (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 689-698 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photochromic molecules such as dihydroindolizines (DHI) containing crown ether units can be ‘tuned’, as far as their properties are concerned, by supramolecular ion binding. Inclusion of the ion in the crown ether cavity yields a new supramolecular species. This species shows special properties of the excited state after guest addition: (a) bathochromic shifts of the photochromic crown ethers and also hyperchromic effects in the UV spectra; (b) fluorescence intensity of one of the photochromic crown ethers is either increased (crown excitation) or decreased (DHI excitation) after addition of alkali metal ions; and (c) in the ground state a large change in reaction rate for the reaction 1,5-electrocyclization betaine (coloured form) to dihydroindolizine is observed in the supramolecular complexes.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610051011
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  • 10
    Electronic Resource
    Electronic Resource
    Significance of the inner-surface structure of small-caliber prosthetic blood vessels in relation to the development, presence, and fate of a neo-intima. A morphological evaluation (1984)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 18 (1984), S. 745-755 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Microvascular prostheses with three different inner surface structures were examined morphologically 1-18 months after implantation to evaluate the presence and structure of the neo-intima. Fibrous polyurethane tubes (length: 5-10 mm, inner diameter: 1.5 mm) were implanted in the rat abdominal aorta in group A with a fibrillar inner structure (pore sizes 20-50 m̈m), and in group B the inner fibrillar structure was coated with an impermeable continuous silicon sheet. Expanded polytetrafluorethylene vascular prostheses (length: 40 mm, inner diameter: 4 mm) were implanted in the dog carotid artery (group C). The specimens were examined by light microscopy and scanning electron microscopy. A continuous and permanent neointima was only found in the prostheses with the porous fibrillar inner structure (group A). The thin new lining sheet was well attached to the prosthetic wall by cellular protrusions. In the silicon-coated prostheses (group B) also a continuous neo-intima had developed which, however, was irregular, thicker, and not anchored to the prosthetic wall. The expanded polytetrafluorethylene prostheses (group C) showed also after 1 year only incomplete lining with a neo-intima. Fresh blood cell deposits could be observed in the unlined prosthetic wall. It is concluded that a continuous lining of vascular grafts with a thin neo-intima is only achieved if the cells invading the prostheses from the anastomotic areas can anchore their cytoplasmic protrusions onto an appropriately structured inner surface. If these anchoring facilities are not provided, the unattached neo-intima will thicken, interfering with the patency of these microvascular prostheses, or fragments of the neo-intima or alternatively mural thrombi may constantly strip off and embolize.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820180705
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