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  • 1
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    Chinese Journal of Plant Ecology
    In:  EPIC3Chinese Journal of Plant Ecology, Chinese Journal of Plant Ecology, 47(10), pp. 1453-1463, ISSN: 1005-264X
    Publication Date: 2024-03-19
    Description: Fossil pollen and spore records provide highly creditable proxy data to investigate the past environmental changes such as palaeovegetation and palaeoclimate. Pollen database promotes past environmental studies from local to regional and global scales and from qualitative to quantitative reconstructions. This is of great significance on exploring the interactions among past vegetation, climates and anthropogenic disturbances at large spatial scale and long temporal scale, to better understand the evolution of the earth system. In this paper, a fossil pollen dataset of China is compiled, by synthesizing 372 original or digitized fossil pollen records including 790 pollen taxa in China’s land and ocean during the late-Quaternary (since 50 ka BP). The dataset includes site names, latitude, longitude and altitude, pollen data source, sample type, sediment length or span, sample number of each site, dating method and dating number, age span and reference, as well as the fossil pollen percentage of each sampling site. The pollen data, mostly published from late 1980s to present, are concentrated in vegetation regions of temperate and subtropical forests, temperate grasslands, temperate deserts and alpine vegetation on the Qingzang Plateau. Sample sites are distributed at different altitudes from deep sea to high Qingzang Plateau, but the majority of the sites are located between 0–2 000 m. The dataset comprises of 178 raw pollen records (47.8%) and 194 digitized pollen records (52.2%). Pollen samples are mainly from lake sediment (151 sites), alluvial/fluvial sediment (99 sites), and peat (67 sites), accounting for 85.2% of the total sampling sites. Radiocarbon is the main dating method that accounts for 93.8% of total samples, and most of the sites have 2–10 radiocarbon dating data. Each site has an average number of pollen taxa of 19, with the most sites having 4–30 pollen taxa. The temporal and spatial distribution of representative pollen taxa (Pinus, Quercus, Artemisia and Poaceae) reveals increasing trends both in their distributional range and pollen concentration from the last glacial maximum to Holocene, but such trends have various regional patterns in different parts of China. This fossil pollen dataset is a fruitful work of collection of pollen records in most territory of China that conducted by palynologists from China and overseas during the last half century. It consolidates the valuable and fundamental data that can be potentially utilized to explore the evolution of past environments and their driving mechanism of climate change and human disturbance.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2538-2540 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new two-color n-type GaAs/AlAs/AlGaAs double barrier quantum well (DBQW) and bound-to-miniband GaAs/AlGaAs quantum well infrared photodetector (QWIP) with photovoltaic (PV) and photoconductive (PC) dual-mode operation in the 3–5 and 8–14 μm atmospheric spectral windows has been demonstrated in this work. It consists of a stack of the midwavelength infrared (MWIR) QWIP and the long-wavelength infrared (LWIR) QWIP. The PV detection scheme uses transition from the ground bound state to the first quasi-bound excited state for the MWIR-QWIP. The PC detection scheme has two different transitions, one identical to the PV mode detection scheme while the other uses transition from the ground bound state to the miniband state of the superlattice barrier LWIR-QWIP. The peak responsivity for the PV mode was found to be 17 mA/W at λp=4.1 μm and T=50 K with a bandwidth Δλ/λp=15%. The peak responsivities for the PC mode were found to be 25 mA/W at λp=4.1 μm, Vb=1.0 V, and 0.12 A/W at λp=11.6 μm, Vb=3.2 V, and at T=50 K, with a bandwidth Δλ/λp=18%. The PV responsivity was found to be 68% of the PC responsivity at λp=4.1 μm and T=50 K, demonstrating the ability for efficient PV mode operation at 3–5 μm by using the DBQW structure. This is the highest ratio reported for the spectral region of 3–5 μm wavelength with a DBQW structure.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1107-1112 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dark current noise measurements between 10 and 105 Hz were carried out at T=77 K on three different types of III-V quantum-well infrared photodetectors designed for 8–12 μm IR detection. These devices have superlattice barriers leading to miniband transport in the extended conduction band. For frequencies between 102 and 104 Hz, noise plateau levels stemming from the trapping and detrapping of electrons in the quantum-well bound states are observed. From the measured noise data the low-bias electron diffusion length, the bias-dependent noise gain, the electron trapping probability, and the thermal electron generation rate are calculated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1486-1490 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dark current noise measurements between 101 and 105 Hz were carried out on a compressively strained p-type InGaAs/AlGaAs quantum-well infrared photodetector as a function of temperature and bias voltage. The measured noise can be attributed to number fluctuation noise associated with the generation and recombination of holes from and to the quantum-well bound states and the extended valence-band states. At low bias the number fluctuation noise translates into current fluctuation noise via hole diffusion, where as at higher-bias values the coupling is via the hole drift current component. Our measurements indicate that the field-induced barrier lowering and the Schottky image effect strongly influence the device characteristics. In addition we observe that the thermally generated heavy holes diffuse, at low fields, on the average to the nearest neighboring quantum well where they subsequently recombine. This recombination process is triggered by hole scattering with the acceptor centers. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6009-6011 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A normal incidence p-type compressive strained-layer In0.4Ga0.6As/GaAs quantum well infrared photodetector (PSL-QWIP) grown on (100) semi-insulting GaAs substrate with molecular beam epitaxy technique for 3–5 μm mid-wavelength infrared and 8–14 μm long-wavelength infrared detection was demonstrated for the first time. This PSL-QWIP shows a broadband double-peak response between 8 and 9 μm wavelength by utilizing the resonant transport coupling mechanism between the heavy-hole type-I states and the light-hole type-II states. Using the compressive strain in the InGaAs quantum well, normal incident absorption was greatly enhanced by reducing the heavy-hole effective mass and increasing density of states of off-zone center. Maximum responsivities of 93 mA/W and 30 mA/W were obtained at peak wavelengths of λp1=8.9 μm and λp3=5.5 μm, respectively, with Vb=1.6 V. Detectivity at λp1=8.9 μm was found to be 4.0×109 cm(square root of)Hz/W at Vb=0.3 V and T=75 K.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 8168-8174 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical analysis of the grating coupling for a two-dimensional circular aperture mesh metal grating coupled GaAs quantum well infrared photodetector (QWIP) has been carried out. The inner products of Floquet modes and waveguide modes were derived in a simple analytic form. Using the normalized wavelength and normalized aperture radius, two sets of universal plots were generated to display the normalized total power and absorption angle of the higher-order diffracted waves versus normalized wavelength for the grating coupler. From these universal plots, the optimum grating parameters for the GaAs QWIPs can be obtained. The results show a 2.7 times enhancement of the responsivity at 10.2 μm wavelength for the circular aperture metal grating coupler over that of the 45° edge-illuminated GaAs QWIP.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6571-6573 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel method of enhancing Schottky barrier height, while reducing the surface-state density on n-type In0.53Ga0.47 As surfaces using P2S5/(NH4)2S and (NH4)2Sx passivation is described in this communication. The current-voltage and capacitance-voltage characteristics show that passivated diodes have lower reverse leakage current and higher effective barrier height than that of the unpassivated diodes. The electrical characteristics of passivated diodes have not changed after one month of exposure to the air.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 6536-6540 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on a new high-speed InP-based InxGa1−xAs Schottky barrier photodiode for infrared detection. The photodiodes were fabricated on both p- and n-InGaAs epilayers. For this application, Schottky barrier height enhancement on InGaAs has been demonstrated. The photodiodes had responsivities as high as 0.55 A/W and quantum efficiencies of up to 45% in the range of 1.3–1.6 μm without antireflection coating. The response speed of photodiodes was measured by the impulse response and autocorrelation methods; rise times of 85 ps for p-InGaAs and 180 ps for n-InGaAs photodiodes were obtained. Recently, a barrier height enhancement of 0.35 eV was obtained in n-InGaAs photodiodes, resulting in a great reduction of leakage currents. This would lead to further improvement in the device performance of the photodiodes. Based on measured RC time constants, we estimate the intrinsic response speed to be 12 GHz for n-InGaAs and 18 GHz for p-InGaAs photodiodes. These results show that InP-based InxGa1−xAs Schottky barrier photodiodes can be very useful for high-speed infrared receivers in fiber-optic communications.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2192-2196 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two normalized parameters (i.e., s=λ/g and h=a/g, where g is the grating period and a is the width of metal dot) are introduced to characterize the two-dimensional (2D) double periodic reflection metal grating coupler for a multiquantum well infrared photodetector (QWIP). The "method of moments'' is used to analyze this square metal grating structure for coupling the normal incident infrared (IR) radiation into the quantum wells. The main advantage for such a grating structure is that the coupling of the normal incident IR radiation is independent of its polarization direction. Two universal graphs relating the higher-order diffracted power and diffracted angle to the normalized wavelength have been constructed for the design of 2D metal grating coupled QWIPs. By using a simple scaling rule, the coupling quantum efficiency versus wavelength over a broad IR spectrum can be obtained for the grating coupled QWIPs.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 582-587 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical analysis of a two-dimensional (2D) square mesh metal grating coupler formed on top of a bound-to-miniband (BTM) transition GaAs-based quantum-well infrared photodetector (QWIP) has been carried out. Two normalized parameters s and h (i.e., s=λ/g and h=a/g, where g is the grating period and a is the width of the aperture) are used in the simulations of the 2D square mesh metal grating structure formed on a GaAs BTM QWIP. Using two universal graphs displaying the total power and diffracted angle of the higher-order transmitted and reflected waves versus normalized wavelength, the optical absorption constant and coupling quantum efficiency of the QWIPs are calculated for different grating periods and aperture sizes in the wavelength range of 8–14 μm. A maximum coupling quantum efficiency of η=52% was obtained for the square mesh metal grating coupled BTM QWIP with g=3.3 μm and a=2 μm, which is higher than that of the 45° polished facet illumination (η=38%).
    Type of Medium: Electronic Resource
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