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  • 1
    Electronic Resource
    Electronic Resource
    High-temperature properties of GaInAs/AlGaAs lasers with improved carrier confinement by short-period superlattice quantum well barriers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2863-2865 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of the carrier confinement on the output characteristics of GaInAs/AlGaAs lasers was investigated. To improve the carrier confinement, AlGaAs/GaAs short-period superlattices were used as quantum well barriers. In comparison to lasers with GaAs barriers the structures with the modified barriers show improved temperature properties at low threshold current densities without deterioration of the internal quantum efficiency (〉95%). High characteristic temperatures (T0) well above 300 K were measured between 20 and 75 °C and laser operation up to 238 °C could be achieved. The large improvement in T0 is mainly attributed to the reduced thermionic emission of carriers out of the quantum well due to the increased barrier height and the carrier reflection above the barrier by the short-period superlattice. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122611
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of the critical current density in grain boundary Josephson junctions on a nanometer scale (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2289-2291 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The critical current Ic of YBa2Cu3O7−δ bicrystal grain boundary Josephson junctions (GBJs) have been measured in high magnetic fields up to B=12 T. Even at the highest applied magnetic fields, Ic varied periodically with varying magnetic field. By comparing the envelope of the measured Ic(B) dependencies to model calculations we obtain information on the spatial distribution of the supercurrent density jc on a length scale down to below 1 nm. Our analysis gives clear evidence that jc has spatial inhomogeneities on all length scales down to 1 nm with a probability distribution p(a) for the characteristic length scale a of the inhomogeneities. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113263
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  • 3
    Electronic Resource
    Electronic Resource
    Electric field controllable Josephson junctions of high quality in high-Tc superconductors (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3031-3033 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three-terminal Josephson junctions, the third terminal of which can be used to control the electronic properties of the device, are the key to a number of exciting device applications of high-Tc superconductors. To this end a novel device structure has been developed, which consists of an inverted metal-insulator-superconductor field-effect transistor into which a bicrystal grain boundary junction is embedded. These devices are excellent Josephson junctions as exemplified by their current–voltage characteristics and the magnetic field dependencies of the critical currents. The critical current of the junctions can be changed by 8% per volt applied to the gate electrode, the gate currents being negligible. Because they are sensitive to electric as well as magnetic fields, the junctions can be controlled by two independent inputs. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115567
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  • 4
    Electronic Resource
    Electronic Resource
    The Effect of NO-Donors in Bovine and Rat Pineal Cells: Stimulation of cGMP and cGMP-Independent Inhibition of Melatonin Synthesis (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neuroendocrinology 7 (1995), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The presence of soluble guanylate cyclase in the pineal and its regulation by adrenergic pathways has been well documented. Recent evidence points to adrenergically stimulated nitric oxide generation as a mechanism for coupling this pathway. To what extent nitric oxide (NO) signalling can influence adrenergically stimulated melatonin synthesis has not been investigated. Cyclic guanosine 3′,5′-monophospate (cGMP) signal transduction in the bovine pineal has also received little attention. We describe in the present report: 1) a dose-dependent elevation of cGMP in response to the nitrovasodilators, sodium nitroprusside (SNP) and 3-morpholino-sydnonimine (SIN-l), 2) a dose-dependent inhibition of melatonin synthesis by SNP and SIN-1, but not by 8-Br-cGMP in both bovine and rat pineal cell cultures, which is not due to cytotoxicity as judged by two different approaches, and 3) immunohistochemical evidence for the presence of nitric oxide synthase (NOS) (EC 1.14.23.-) in the intact bovine pineal gland and in cultured bovine pinealocytes. These data support the view that NOS is a component of the cGMP-generating system in mammalian pinealocytes. Although NO-donor molecules are also potent activators of cGMP accumulation, they may have other important actions in the pineal, namely the inhibition of adrenergic-stimulated melatonin synthesis. As SNP and SIN-1 exerted this inhibitory effect on cells regardless of whether they were stimulated by isoproterenol, forskolin or 8-Br-CAMP it would appear that NO-donors can act ‘downstream’ from the receptor/adenylate cyclase level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2826.1995.tb00749.x
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  • 5
    Electronic Resource
    Electronic Resource
    NADPH-diaphorase and NOS enzymatic activities in some neurons of reptilian gut and their relationships with two neuropeptides (1999)
    Springer
    Anatomy and embryology 199 (1999), S. 397-405 
    Details
    ISSN: 1432-0568
    Keywords: Key words Reptiles ; Gastrointestinal tract ; Nitric oxide ; VIP ; Galanin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The distribution of neurons containing the enzymes NADPH-diaphorase (NADPH-d) and nitric oxide synthase (NOS) has been studied in the gastrointestinal tract of lizard (Podarcis s. sicula) and snake (Thamnophis sirtalis). The techniques employed were the NADPH-d/nitroblue tetrazolium histochemical method, and the indirect immunofluorescence applied to cryostat sections and to whole-mount preparations. The colocalization of NADPH-d with NOS, with vasoactive intestinal polypeptide (VIP) and with galanin (Gal) was also studied, and a Western blot analysis using an antibody directed against mammalian Gal was performed on lizard stomach extracts. NADPH-d positive nerve cell bodies and fibres were found in the myenteric and submucous plexuses throughout the gastrointestinal tract of both reptiles. These nerve structures were also present in the other intramural nerve plexuses, although in smaller quantities. Both in lizard and snake, the stomach revealed a positive nerve population that was more dense than elsewhere in the gut. The population of the NADPH-d-positive neurons observed in the lizard was larger than that observed in the snake. The distribution of both populations was similar to those that have been described in the gut of several mammalian and non-mammalian vertebrates. Both in lizard and snake, a one-to-one correspondence was noted between NOS- and NADPH-d-containing nerve cell bodies, and the nitrergic neurons containing Gal appeared to be more numerous than those containing VIP. Western blot analysis recognised a single band with a molecular weight (3.4 kDa) very similar to that of porcine Gal. It is hypothesised that at least some of the nitrergic neurons of the lizard and snake gut are inhibitory motor neurons innervating the circular smooth musculature. In addition, the colocalization of NOS and VIP in neurons enhances their inhibitory action. The role of the neurons containing both NOS and Gal remains unknown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004290050238
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  • 6
    Electronic Resource
    Electronic Resource
    In search of a function for tetrahydrobiopterin in the biosynthesis of nitric oxide (1995)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 351 (1995), S. 453-463 
    Details
    ISSN: 1432-1912
    Keywords: Key wordsNitric oxide synthase ; Tetrahydrobiopterin ; Pteridine metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract (6R)-5,6,7,8-Tetrahydro-L-biopterin (H4biopterin) is well known as a cofactor of enzymes that hydroxylate aromatic amino acids. More recent work has revealed an essential role of H4biopterin in the biosynthesis of nitric oxide (NO), an intercellular messenger molecule synthesized from L-arginine by different NO synthase isozymes in many species and tissues. While the function of H4biopterin in aromatic amino acid hydroxylation is well established, the role of this pteridine in NO synthesis is, as yet, elusive. Current experimental evidence hints at a dual mode of action of H4biopterin, involving both an allosteric effect on the NO synthase protein and participation as a reactant in L-arginine oxidation. As discussed in detail in the present article, the latter effect of this pteridine may be related to the protection of NO synthase from feedback inhibition by NO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00171035
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  • 7
    Electronic Resource
    Electronic Resource
    Nitric oxide synthases: catalytic function and progress towards selective inhibition (1998)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 358 (1998), S. 127-133 
    Details
    ISSN: 1432-1912
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Biosynthesis of nitric oxide (NO) is performed by the dimeric, heme-containing enzyme nitric oxide synthase, which requires the flavins FAD and FMN, as well as the pteridine cofactor (6R)-5,6,7,8-tetrahydro-L-biopterin (H4biopterin) in order to catalyze the NADPH-dependent oxidation of L-arginine. The three major isoforms of nitric oxide synthase (NOS), although identical in that they contain a carboxy-terminal reductase and an amino-terminal oxygenase domain, fulfill diverse physiological functions, according to their differing expression patterns and mechanisms of activation. The pteridine H4biopterin, which affects both the conformational stability and activity of NOS, demonstrates anticooperative binding which results in the stoichiometric production of NO and O2 –. Physiological mechanisms involving superoxide dismutase and reduced glutathione exist to avoid the subsequent formation of the potent oxidant peroxynitrite. With regard to inhibition of NO production, novel isoform-selective inhibitors are proving useful not only for dissecting the physiological functions of NOS, but also in the development of novel therapeutic agents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00005233
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  • 8
    Electronic Resource
    Electronic Resource
    Transformation of simulated wet sulfate deposition in forest soils assessed by a core experiment using stable sulfur isotopes (1995)
    Springer
    Water, air & soil pollution 79 (1995), S. 243-260 
    Details
    ISSN: 1573-2932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The effects of elevated atmospheric SO 4 2− deposition on S cycling in forest soils were assessed in an irrigation experiment using stable S isotopes. Over a period of 20 months, core lysimeters of five acidic forest soils from Southern Germany with different parent material and pedogenesis were irrigated with solutions chemically similar to canopy throughfall. Sulfate deposition in three experimental variants corresponded to 23, 42 and 87 kg S ha−1 yr−1. The SO 4 2− used for irrigation had aδ 34S ratio of +28.0‰ CDT (Canon Diablo Troilite standard), differing by more than +25‰ from natural and anthropogenic S in Southern Germany. A combination of chemical and isotopic analyses of soil and seepage water samples was used to elucidate the fluxes and transformations of simulated wet SO 4 2− deposition in each soil core. Retention of experimentally deposited S ranged from 57±5% in coarse-grained soils low in sesquioxides and clay, to 80±8% in loamy soils with high sesquioxide content. The sesquioxide content proved to be the major factor governing S retention. The ratio of S retained as inorganic SO 4 2− (mainly by adsorption) to that incorporated into organic compounds (presumably by microbial synthesis) ranged from 2 to 4. For the organic S pool, the amount of S retained as C-bonded S exceeded by far that immobilized as ester sulfate in four of the five soils. Application of34S-enriched SO 4 2− appears to be a suitable experimental tool to assess fluxes and transformations of deposited S in forest soils, if aerobic conditions are maintained. In contrast to radioactive S tracers, the concept should be applicable not only in laboratory and lysimeter experiments, but also in long term studies of whole forest ecosystems (e.g., experimental watersheds).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01100440
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  • 9
    Electronic Resource
    Electronic Resource
    Selective assembly of cyclodextrins on poly(ethylene oxide)–poly(propylene oxide) block copolymers (1999)
    Springer
    Journal of computer aided molecular design 13 (1999), S. 373-383 
    Details
    ISSN: 1573-4951
    Keywords: host–guest complexes ; molecular necklace ; molecular recognition ; molecular self-assembly ; molecular solvation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper presents a computational study on the formation of a molecular necklace formed by specific threading of cyclodextrins (CDs) on block copolymers. Structural as well as energetic principles for the selective complexation of α- and β-cyclodextrin with poly(ethylene oxide)–poly(propylene oxide) block copolymers (PEO–PPO) are elucidated considering a diblock copolymer of equimolecular composition (PEO)4–(PPO)4 as guest. A non-statistical distribution of CDs, i.e. α-CDs primarily located on the PEO chain and β-CDs on PPO blocks of the polymer, is based on a variety of structural features and energetic preferences considering both potential as well as solvation energies. This selectivity becomes already obvious considering 1:1 complexes between PEO and PPO monomers and the two CDs, but is increasingly evident when calculating higher order ensembles. Besides the host–guest interaction, docking between CDs themselves is an important, also non-statistical, prerequisite for the self-assembly of highly ordered tubes. The formation of intermolecular hydrogen bonds between adjacent CDs in a tubular aggregate gives an important contribution to the overall stability of the molecular necklace. The net effect, based on the preferential interaction between host and guest as well as between the host molecules themselves, results in the formation of a stable, highly ordered macromolecular, multicomponent aggregate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008095501870
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  • 10
    Electronic Resource
    Electronic Resource
    Nitric oxide/cGMP pathway components in the Leydig cells of the human testis (1996)
    Springer
    Cell & tissue research 287 (1996), S. 161-170 
    Details
    ISSN: 1432-0878
    Keywords: Key words: NO/cGMP pathway ; Testis ; Leydig cells ; Immunocytochemistry ; RIA ; Cell culture ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. In this study we sought to determine whether the main components of the nitric oxide (NO) pathway are localized within the Leydig cells of the human testis and whether the soluble guanylyl cyclase (sGC), the enzyme that accounts for NO effects, is functionally active in these cells. Using an amplified immunocytochemical technique, immunoreactivity for nitric oxide synthase (NOS-I), sGC and cyclic guanosine monophosphate (cGMP) was detected within the cytoplasm of human Leydig cells. Distinct differences in staining intensity were found between individual Leydig cells, between cell groups and between Leydig cells of different patients. By means of a specific cGMP-RIA, a concentration-dependent increase in the quantity of cGMP was measured in primary cultures of human Leydig cells following exposure to the NO donor sodium nitroprusside. In addition, NOS-I immunoreactivity was seen in Sertoli cells, whereas cGMP and sGC immunoreactivity was found in Sertoli cells, some apically situated spermatids and residual bodies of seminiferous tubules. Dual-labelling studies and the staining of consecutive sections showed that there are several populations of Leydig cells in the human testis. Most cells were immunoreactive for NOS-I, sGC and cGMP, but smaller numbers of cells were unlabelled by any of the antibodies used, or labelled for NOS-I or cGMP alone, for sGC and cGMP, or for NOS-I and sGC. These results show that the Leydig cells possess both the enzyme by which NO is produced and the active enzyme which mediates the NO effects. There are different Leydig cell populations that probably reflect variations in their functional (steroidogenic) activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410050742
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