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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 614-621 
    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
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 28-31 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A target of gaseous polarized hydrogen was formed by injecting polarized hydrogen atoms (produced by Stern–Gerlach spin separation) into a storage cell consisting of a cylindrical tube open at both ends. The target was placed in a storage ring to study the target characteristics (nuclear polarization, target thickness, radiation resistance). A weak transverse guide field (5 G) was applied to define the polarization direction. When atoms in a single hyperfine state were selected, the nuclear polarization of the target was measured to be 0.80±0.02. The areal density of the target under these conditions was (5.5±0.2)×1013 H/cm2, while for two spin states (applicable to experiments in high energy rings where a strong magnetic field can be applied to the target) the target thickness was found to be (8.2±0.3)×1013 H/cm2. The target polarization was unaffected by prolonged exposure of the target to beams up to 1 mA. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 135-137 
    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
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  • 4
    ISSN: 1432-0649
    Keywords: 42.60 ; 42.55 ; 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We systematically investigate the difference between both actively and passively mode-locked lasers with Gain-at-the-End (GE) and Gain-in-the-Middle (GM) at the example of Nd:YLF lasers. The GE laser generates pulse widths approximately three times shorter than a comparable GM cavity. This is due to enhanced Spatial Hole Burning (SHB) which effectively flattens the saturated gain and allows for a larger lasing bandwidth compared to a GM cavity. We first investigate enhanced SHB by measuring the cw mode spectrum, where we have observed that the mode spacing in GE cavities depends primarily on the crystal length. This was also confirmed for a Nd:LSB crystal, where the pump absorption length was significantly shorter than the crystal length. In mode-locked operation, pulse widths of 4 ps for passive mode locking and 5 ps for active mode locking are demonstrated with GE cavities, compared to 11 ps for passive and 17 ps for active mode locking with GM cavities. Additionally, the time-bandwidth product for the GE cavity is approximately twice the ideal product for a sech2 pulse shape and cannot be improved by dispersion compensation alone, while the GM cavity has nearly ideal time-bandwidth-limited performance. The results for the GM cavity compare well to existing theories taking into account the added effect of pump-power-dependent gain bandwidth which increases the bandwidth of Nd: YLF from 360 to 〉 500 GHz. In a following paper [1] (called Part II) a rigorous theoretical treatment of the effects due to SHB will be presented.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 61 (1995), S. 569-579 
    ISSN: 1432-0649
    Keywords: 42.60 ; 42.55 ; 42.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In Part I of this paper [1] experimental results were presented and discussed. In this part, we investigate theoretically the dynamics of end-pumped solid-state lasers due to enhanced spatial hole burning. This becomes possible by a fast numerical implementation of the saturated gain in the presence of strong spatial hole burning that allows to treat the multimode case for an arbitrary pumping level. We find for a wide range of laser parameters that the mode spacing of the cw running modes is essentially determined by the length of the gain medium and only weakly depends on the absorption depth of the pump transition. It is shown that spatial hole burning can lead to a completely flat saturated gain profile over half of the gain bandwidth. In mode-locked lasers, the flat gain due to spatial hole burning results in shorter pulses. But the pulses are neither Gaussian-nor sech-shaped as they are in actively or passively mode-locked lasers without spatial hole burning. Further, we show that soliton-like pulse shaping can be used to restore a transform-limited sech-shaped pulse in an end-pumped solid-state laser while exploiting the full gain bandwidth of the laser material.
    Type of Medium: Electronic Resource
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  • 6
    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
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 86 (1931), S. 258-261 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1435-1420
    Keywords: Key words Toxic shock-like syndrome (TSLS) ; necrotizing fascitis ; streptococcus pyogenes ; puerperal sepsis ; Schlüsselwörter Toxic shock-like syndrome (TSLS) ; nekrotisierende Fasziitis ; Streptococcus pyogenes ; puerperale Sepsis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Seit Mitte der achtziger Jahre häufen sich weltweit Berichte über invasive Infektionen verursacht durch Streptococcus pyogenes. In einer retrospektiven Studie wurden Häufigkeit, Symptomatik, Verlauf, Therapiemöglichkeiten und mikrobiologische Charakterisierung der Erkrankung untersucht. In die Studie wurden alle zehn Patienten (sieben weibliche/drei männliche, Durchschnittsalter 45,0 [4–71] Jahre) des Kreiskrankenhauses Reutlingen eingeschlossen, bei denen zwischen September 1994 und Mai 1996 Streptococcus pyogenes an sterilen Entnahmeorten nachgewiesen wurde. Die Isolate wurden am damaligen Nationalen Referenzzentrum (Jena) bezüglich Typisierung und Toxinbestimmung analysiert. Bezogen auf die ca. 272000 Einwohner des Landkreises Reutlingen liegen unsere Zahlen für invasive Infektionen im Bereich der in Nordamerika anhand von Populationsstudien ermittelten Daten (Inzidenzen zwischen 1,5–4,3/100000). Bei sieben Patienten war vor der akuten Krankheitsverschlechterung eine grippeähnliche Prodromalsymptomatik zu beobachten. Auffällig war eine Häufung des schwer verlaufenden „toxic shock-like syndrome“ (TSLS) mit den Kriterien: Schocksymptomatik, Multiorganversagen, Weichteilnekrose und generalisiertes Erythem (n=6). Alle überlebenden Patienten mit TSLS mußten mit mehrtägiger Respiratortherapie behandelt werden (7–16 Tage). Eine Patientin mit TSLS starb am Aufnahmetag aufgrund eines fulminanten septischen Schocks. Die Analyse der isolierten Stämme zeigte kein einheitliches Bild bezüglich der Serotypen und der Toxinbildung. Folgende sofortige therapeutische Maßnahmen sind erforderlich: antibiotische Behandlung, chirurgische Sanierung des Infektherdes und typische Intensivtherapie bei Multiorganversagen. Die beobachtete Prodromalsymptomatik unterstreicht nachdrücklich die Möglichkeit eines frühzeitigen Eingreifens in das Krankheitsgeschehen.
    Notes: Summary Since the middle of the 1980s,? reports of invasive infections caused by streptococcus pyogenes are increasing world wide. In a retrospective study the frequency, symptoms, course, therapeutic possibilities, and microbiological characterization of this disease were examined. In the study, all 10 patients (seven females/ three males, average age 45.0 [4–71]) of the district hospital of Reutlingen were included who had a proven streptococcus pyogenes infection between Sept. 1994 and May 1996, defined by isolation of group A streptococci from a sterile site. Isolates were analyzed for serotype and production of exotoxins in the National Reference Center (Jena) of that time. In relation to the approx. 272,000 inhabitants of the district of Reutlingen, our numbers for invasive infections are within the range of the data established in the USA on population-based studies (incidence between 1.5 to 4.3 per 100,000). In seven patients,? influenza-like symptoms were observed previous to the acute deterioration of the disease. There was a conspicuous accumulation of the severe courses of toxic shock-like syndrome (TSLS) with the following criteria: shock, multiorgan failure, soft tissue necrosis, and generalized erythema (n=6). All surviving patients with TSLS had to be treated during several days with assisted respiration (7–16 days). One female patient with TSLS died on the day of admittance due to an intensive septic shock. In the analysis of the isolated strains,? no uniform results regarding the serotypes and the production of exotoxins were found. The following therapeutic measures are required immediately: antibiotic treatment, surgical treatment of the infective focus, and the established intensive care therapy in cases with multiorgan failure. The observed prodromal symptoms underline emphatically the possibility of an early intervention in the course of the disease.
    Type of Medium: Electronic Resource
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  • 9
    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
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