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  • Springer  (4)
  • 1
    ISSN: 1432-0630
    Keywords: 6855 ; 7280E ; 7340L
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Modulation doped Al0.3Ga0.7As/In x Ga1−x As/GaAs high electron mobility transistor structures for device application have been grown using molecular beam epitaxy. Initially the critical layer thickness for InAs mole fractions up to 0.5 was investigated. For InAs mole fractions up to 0.35 good agreement with theoretical considerations was observed. For higher InAs mole fractions disagreement occurred due to a strong decrease of the critical layer thickness. The carrier concentration for Al0.3Ga0.7As/In x Ga1−x As/GaAs high electron mobility transistor structures with a constant In x Ga1−x As quantum well width was investigated as a function of InAs mole fraction. If the In x Ga1−x As quantum well width is grown at the critical layer thickness the maximum carrier concentration is obtained for an InAs mole fraction of 0.37. A considerable higher carrier concentration in comparison to single-sided δ-doped structures was obtained for the structures with δ-doping on both sides of the In x Ga1−x As quantum well. Al0.3Ga0.7As/In x Ga1−x As/GaAs high electron mobility transistor structures with InAs mole fractions in the range 0–0.35 were fabricated for device application. For the presented field effect transistors best device performance was obtained for InAs mole fractions in the range 0.25–0.3. For the field effect transistors with an InAs mole fraction of 0.25 and a gate length of 0.15 μm a f T of 115 GHz was measured.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Neutron scattering has been employed to study the crystalline electric field (CEF) interaction at the Ho3+ site in Bi2Sr2Ca0.5Ho0.5Cu2O8+x. The observed energy spectra exhibit a large number of broad but well-resolved CEF transitions between 1.2 and 73 meV, so that we have been able to unambiguously determine all nine CEF parameters required for the average orthorhombic symmetry. The unusually large line widths of the CEF transitions are shown to be related to the modulated structure. The CEF potential is essentially governed by the charge distribution of the CuO2 planes which turns out to be very similar as in HoBa2Cu3O7-x.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1420-9071
    Keywords: Dietary fibre ; nutrition ; review ; health ; cholesterol ; minerals ; fermentation ; gastrointestinal tract ; cancer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Fibrous material is an integral part of the daily diet, and it exerts direct physiological effects throughout the gastrointestinal tract, in addition to affecting metabolic activities more indirectly. The interplay of these effects is responsible for the presumed desirable influence of fibre on weight regulation, carbohydrate and lipid metabolism, and on colon function. Numerous mechanisms of action have been identified which are related to the type and the physicochemical nature of the fibre. This review concentrates mainly on the serum cholesterol-lowering effect of dietary fibre, its colonic fermentation, and finally on some possible adverse effects that one should be aware of when consuming high amounts of dietary fibre.
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  • 4
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Technik der Wärmeleitungs-Kalorimetrie wurde zur Untersuchung des thermischen Verhaltens von verschiedenen Kohlenhydraten zwischen 20°C und 270°C eingesetzt. Die Muster wurden in dicht verschlossenen Kapseln erhitzt. Der Temperaturbereich, in welchem exotherme Reaktionen infolge thermischer Zersetzung abliefen, änderte sich stark in Abhängigkeit vom untersuchten Kohlenhydrattyp. Reaktionsenthalpien von 44 Zuckern und Polysacchariden wurden ermittelt. Endotherme Phänomene, wie das Schmelzen oder das Verdampfen von Kristallwasser wurden auch beobachtet. Schmelztemperaturen und Schmelzenthalpien von 34 Zuckern und Zuckeralkoholen sind tabelliert. Kalorimetrische Daten der Kristallisation amorpher Saccharose, Cellobiose und Lactose werden diskutiert.
    Abstract: Резюме Метод калориметрии т еплового потока был использован для изуч ения термического поведения различных углеводов между 20 и 270°C. О бразцы анализировались наг ревом в закрытых ячейках. Вс ледствии термическо го разложения, интервал температур эксотерм ических реакций изменялся в ш ироких пределах в зав исимости от типа исследуемого углевода. Приведены э нтальпии реакций для 44 сахаров и полисахаридов. Наблю дались такие эндотермическ ие явления, как плавле ние или испарение кристалли зационной воды. Приведены температу ры плавления и энталь пии для 34 сахаров и многоатомн ых спиртов. Представлены калори метрические кривые, п оказывающие кристаллизацию амор фной сахарозы, целлобиозы и лактозы.
    Notes: Abstract The technique of heat flow calorimetry was used to study the thermal behaviour of different carbohydrates between 20°C and 270°C. The samples were analyzed by heating in sealed cells. The temperature range in which exothermic reactions, due to thermal decomposition, occurred varied widely depending on the type of carbohydrate investigated. Reaction enthalpies of 44 sugars and polysaccharides are given. Endothermic phenomena, such as fusion or vaporization of crystallized water, were also observed: fusion temperatures and enthalpies of 34 sugars and sugar alcohols are listed. Calorimetric curves showing crystallization of amorphous sucrose, cellobiose and lactose are also presented.
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