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  • 1
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    Using isotopes in a multi-proxy approach to understand groundwater-surface water interactions in a drought sensitive catchment (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-09-12
    Description: The frequency and intensity of droughts have increased due to climate change, providing an urgent impetus to improve understanding of ecohydrological fluxes in drought-sensitive areas where water and food security are threatened. We used isotopes as core tools in assessing the effects of land use and catchment properties on groundwater recharge during a prolonged drought starting in summer 2018 in a 66 km2 lowland, mixed land use catchment (Demnitzer Mill Creek, Germany). This used water stable isotopes, along with radioactive isotopes, hydrogeochemical tracers, water table observations and geophysical investigations to quantify the spatial and temporal patterns of groundwater recharge. Long-term groundwater level data showed a declining trend since 2011, which accelerated after 2018 and resulted in increasingly intermittent stream flows from the catchment. Geophysical surveys indicated shallow water tables (typically 〈3m deep) in low permeability drift are generally recharged during winter, leading to higher groundwater–surface water connectivity which is the first order control on stream flow generation. This was supported by similar geochemical characteristics of groundwater and stream flow. Isotopic mass balances showed that evapotranspiration varied with land cover, being highest under forests and lowest under crops; with recharge correspondingly being lower and older (~5 years) under forests and higher and younger (~3 years) under crops. Groundwater age estimates using tritium indicated high uncertainty but indicated that shallow groundwater was 〈10 years old and similar to stream flow. Such multi-proxy approaches help understand changes in ecohydrological processes during droughts and develop sustainable land and water management strategies for climate change.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 2
    Electronic Resource
    Electronic Resource
    Thermoinduced and photoinduced reactions of NO on Si(111)7×7. III. Photoreaction mechanisms (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 9089-9095 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relative yield of photoinduced desorption from NO-exposed Si(111)7×7 has been measured as a function of photon power, wavelength, polarization, incident angle, and coverage of coadsorbed potassium. The results are analyzed in terms of two possible mechanisms: direct photoelectronic excitation of the NO-surface complex and interaction of hot carriers photogenerated in the substrate with the NO-surface complex. The substrate-mediated mechanism is found to be principally responsible for the photoreactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459199
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanisms of laser interaction with metal carbonyls adsorbed on Si(111)7×7: Thermal vs photoelectronic effects (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4957-4978 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ultrahigh vacuum studies of the interaction of 514 nm radiation from a cw Ar ion laser and its second harmonic at 257 nm with mono- and multilayer coverages of Mo(CO)6, W(CO)6, and Fe(CO)5 adsorbed on Si(111)7×7 at 90 K using thermal desorption spectroscopy (TDS), laser induced desorption spectroscopy, high resolution electron energy loss spectroscopy (HREELS), and Auger electron spectroscopy were performed. A model for the temperature rise of the sample due to cw laser heating is developed. By directly measuring the substrate temperature, these experiments were able to distinguish between photoelectronic and thermal effects active in the decomposition and desorption mechanisms of the adsorbed carbonyls. Results from TDS and HREELS show that Mo(CO)6 and W(CO)6 are molecularly adsorbed, while Fe(CO)5 partially dissociates upon adsorption. The decomposition of adsorbed Mo(CO)6 is caused by electronic excitation due to direct absorption of the 257 nm radiation. Irradiation with 514 nm radiation results in no photochemistry. The same mechanism is dominant for adsorbed W(CO)6 and Fe(CO)5; however, new excitation mechanisms are available to these molecules that lead to bonding changes in W(CO)6 and Fe(CO)5 with 514 nm irradiation. The photodecomposition products of the adsorbed carbonyls are found to be different from the gas-phase decomposition products. The surface stabilizes the adsorbed carbonyls, preventing complete removal of all the CO ligands. Desorption of CO due to photoelectronic excitation is found to occur via sequential single photon absorption and extraction of CO ligands. Evidence of clustering of carbonyl fragments was observed after 257 nm irradiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452667
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  • 4
    Electronic Resource
    Electronic Resource
    Photodissociation of adsorbed Mo(CO)6 induced by direct photoexcitation and hot electron attachment. I. Surface chemistry (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 9077-9088 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adsorption and photodissociation of Mo(CO)6 on potassium-free and potassium-preadsorbed Cu(111) and Si(111)7×7 have been studied under ultrahigh vacuum conditions using vibrational spectroscopy and mass spectrometry. It has been observed that Mo(CO)6 adsorbs molecularly on potassium-free Cu(111) and Si(111)7×7 at 85 K and, upon heating, desorbs at 200 K. In the case of Cu(111), heating also leads to thermal dissociation of a fraction of Mo(CO)6 at ∼150 K. The dissociation channel competes favorably with the molecular desorption channel at low Mo(CO)6 exposures. On potassium-preadsorbed Cu(111) and Si(111)7×7 at 85 K, Mo(CO)6 adsorbs in part molecularly and in part dissociatively. The extent of dissociation depends on the K coverage; a high K coverage results in large degree of dissociation. The thermal desorption temperature for the molecularly adsorbed Mo(CO)6 increases to 210 K on the potassium-preadsorbed surfaces. Adsorbed Mo(CO)6 molecules photodissociate nonthermally into CO and carbonyl fragments. The product CO desorbs under irradiation. Photodissociation occurs on the K-free surfaces only under ultraviolet (UV) irradiation. With coadsorbed potassium, however, the photoyield increases substantially in the UV and extends to the visible and infrared (IR) regions. The carbonyl fragments which are present on the K-preadsorbed surfaces before irradiation are found to have a negligible contribution to the CO desorption signal. The photoactive species is identified to be the molecularly adsorbed Mo(CO)6 .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459706
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  • 5
    Electronic Resource
    Electronic Resource
    Thermoinduced and photoinduced reactions of NO on Si(111)7×7. II. Effects of potassium coadsorption (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5050-5058 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adsorption, thermoreactions, and photoreactions of NO coadsorbed with potassium on Si(111)7×7 at 90 K have been investigated using work-function measurements, high-resolution electron energy loss spectroscopy, and mass spectrometry. A minimum in the work function of Si(111)7×7 at 90 K vs the potassium exposure is observed and it is suggested that higher K exposures passed the work-function minimum result in the formation of K multilayers, which upon thermal heating desorb at 315 K. Submonolayers of potassium introduce a new adsorption configuration of NO on Si(111)7×7 at 90 K. This new NO species exhibits a weak intramolecular bonding and competes with NO adsorbed in other configurations. During thermal heating, this NO species gradually dissociates, thus contributing to N2 recombinative desorption, and at relatively high K coverages leads to desorption of N2 and N2O at 555 K via N2O synthesis from NO. The surface after thermal heating to 〉555 K is depleted of molecular species and covered with atomic N and O. Preferential surface oxidation occurs in the presence of potassium. Under photon irradiation (300–900 nm), desorption of N2, NO, and N2O is observed. The photodesorption intensities decrease monotonically as the K coverage increases. The experiments provide further evidence that the dominant contribution to the three photodesorbed species comes from molecularly adsorbed NO and that N2O is synthesized under photon irradiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457597
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  • 6
    Electronic Resource
    Electronic Resource
    Thermo- and photo-induced reactions of NO on Si(111)7×7. I. Adsorption and chemical reactions (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2689-2705 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adsorption of NO on Si(111)7×7 at 90 K and the subsequent reactions induced by thermal heating and photon irradiation have been investigated in detail, using high-resolution electron energy loss spectroscopy and mass spectrometry. It is found that, in addition to molecular and dissociative adsorption of NO, N2O is produced from NO on Si(111)7×7 at 90 K. The product N2O physisorbs on the surface and, at 110 K, partially desorbs and partially dissociates into N2 and O. Molecular adsorption of NO exists in two independent, presumable bridge and atop configurations. There is no observable conversion between the two forms of molecularly adsorbed NO. At 147 K, the bridge NO is thermally activated, which leads to simultaneous NO desorption and, to a much larger extent, N2O synthesis. Dissociation of bridge NO also occurs at about 147 K, at least at low NO exposures. The atop NO is not involved in the thermal reactions at 147 K, but dissociates between 200 and 300 K. Photon irradiation in the UV, visible, and IR induces desorption and dissociation of NO on Si(111)7×7 at 90 K via nonthermal mechanisms. Furthermore, evidence for photosynthesis of N2O on the surface is observed. It is suggested that the N2O synthesis during thermal heating and photon irradiation proceeds via reaction between an adsorbed NO molecule and a hot N atom produced from NO dissociation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456979
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular cloning and expression of cDNAs encoding rat aldosterone synthase: Variants of cytochrome P-450"1"1"β
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 169 (1990), S. 245-252 
    Details
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0006-291X(90)91460-A
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  • 8
    Electronic Resource
    Electronic Resource
    Enhanced expression of group II phospholipase A"2 in human hepatocellular carcinoma
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Molecular Basis of Disease 1226 (1994), S. 201-205 
    Details
    ISSN: 0925-4439
    Keywords: Group II phospholipase A"2 ; Human hepatocellular carcinoma ; Overexpression ; Phosphatidylglycerol
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0925-4439(94)90029-9
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  • 9
    Electronic Resource
    Electronic Resource
    Assay of the Acetyl-CoA Probe Acetyl-Sulfamethoxazole and of Sulfamethoxazole by Gas Chromatography-Mass Spectrometry
    Amsterdam : Elsevier
    Analytical Biochemistry 212 (1993), S. 481-486 
    Details
    ISSN: 0003-2697
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/abio.1993.1357
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  • 10
    Electronic Resource
    Electronic Resource
    Optical interference in second-harmonic generation from a metal surface with molecular adlayers (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 7058-7063 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A strong oscillation pattern was observed in optical second-harmonic generation (SHG) at a Ag(111) surface under pyridine adlayers with variable thickness. This oscillation appears only when s-, but not p-, polarized fundamental light is used. This effect is attributed to the modulation of the radiation efficiency of the fundamental light penetrating into the Ag bulk and of the second-harmonic light radiating out to the vacuum by pyridine overlayers through optical interference. A standard optical interference model has been developed to quantitatively analyze the oscillation patterns and determine the adlayer thickness. It was found that at 90 K the pyridine overlayer growth rate is 1.4 A(ring) per Langmuir exposure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468331
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