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51.
Polycrystalline silicon wafers were etched in dc discharges of SF6. SFx species were extracted from the discharges and measured with a mass spectrometer. A systematic procedure was used to measure the SF x + signals such that they are indicators of events in the discharge close to the sample undergoing etching. The picture that emerges is remarkably simple and shows the relative stability of several SFx species including SF6, SF4, SF2, and SF which are shown to be extracted from the discharge both in the presence and absence of the silicon sample. When silicon is being etched on the cathode of the discharge cell, the only significant additional products are SiF4 and S2F2. A comparison of blank and sample data for opposite substrate polarities shows that there is only a small cation-assisted etching effect and suggests that ions do not play an important role in the etching of silicon by SF6 discharges.  相似文献   
52.
53.
In this contribution we discuss the thermodynamic behaviour of Hubbard chains with an additional site-diagonal interaction. It is shown rigorously that the strong coupling limit is equivalent to a generalized anisotropic Heisenberg system, which in some recently discussed limiting cases degenerates to an Ising orX-Y system. The whole procedure also works for a collection of chains with interchain interaction, thus it is not restricted to strictly one-dimensional systems. The effect of a magnetic field is discussed, and the results are compared with a recent perturbation approach by using numerical results for the anisotropic Heisenberg chain.  相似文献   
54.
The excitations connected with quantum condensation of a fermion gas are calculated quantitatively along the lines of a previous paper. We find exact agreement with earlier results: excitations of the phonon type in the absence of Coulomb interaction, strong indications for their nonexistence in the presence of this interaction.  相似文献   
55.
    
Ohne Zusammenfassung  相似文献   
56.
Zusammenfassung Mit Hilfe des Torsionsschwingungsversuchs wurde an Phenolharzpreßmassen der Einfluß verschiedener Zusatzstoffe (Glaskugeln unterschiedlicher Korngröße, Gesteinsmehl, Zeolithe) auf den Schubmodul und die mechanische Dämpfung im Temperaturbereich von –180°C bis +240°C untersucht.Mit steigendem Füllstoffanteil wurde eine Erhöhung der Speicher- und Verlustmodulwerte festgestellt, wobei das mechanisch-dynamische Verhalten der gefüllten Proben auch bei höherem Gehalt an Füllstoff deutlich vom viskoelastischen Verhalten des Grundwerkstoffs bestimmt wird.Die Untersuchungen haben gezeigt, daß neben der Konzentration, der Art und der Gestalt der Zusatzstoffe auch die Größe der Füllstoffteilchen und deren Haftung mit der Harzmatrix die wichtigsten Einflußgrößen für die mechanischen Eigenschaften von Phenolharz-Verbundwerkstoffen darstellen.Ein Vergleich der erzielten Meßergebnisse mit den theoretischen Voraussagen über die Schubmodulerhöhung von Teilchenverbundsystemen ergab eine recht befriedigende Übereinstimmung. Wesentlich erscheint, daß bei allen derartigen Verbundsystemen die Korngröße und die Korngrößenverteilung im Bereich um 10–3 mm bis 10–4 mm liegen sollte.
Summary The effect of various inorganic fillers (glass beads of different particle size range, barium sulfate powder, zeolites) on the dynamic-mechanical properties at about 1 Hz of phenol-formaldehyde thermosets have been determined over a range of temperatures from –180°C to +240°C. Increasing the filler content of the specimens increased the storage and loss moduli. In all cases the mechanical behaviour of the composites is dominated by the viscoelastic properties of the resin matrix. The experimental results are compared with theoretical predictions for shear moduli vs. filler content, as known from publications.


Vorgetragen auf der Jahrestagung der Deutschen Rheologen in Berlin vom 28.–30. April 1975.

Mit 19 Abbildungen und 1 Tabelle  相似文献   
57.
A method is described using integrated optics to perform high data rate a.d. conversion. The approach uses the bulk acousto-optic interaction in optical waveguides, with a segmented transducer array to deflect light in response to an analogue signal applied to phase-shifting elements at the transducer.  相似文献   
58.
Macrocyclic natural products often display remarkable biological activities, and many of these compounds (or their derivatives) are used as drugs. The chemical diversity of these compounds is immense and may provide inspiration for innovative drug design. Therefore, a database of naturally occurring macrocycles was analyzed for ring size, molecular weight distribution, and the frequency of some common substructural motifs. The underlying principles of the chemical diversity are reviewed in terms of biosynthetic origin and natures strategies for diversity and complexity generation in relation to the structural diversity and similarities found in the macrocycle database. Finally, it is suggested that synthetic chemists should use not only natures molecules, but also natures strategies as a source of inspiration. To illustrate this, the biosynthesis of macrocycles by non-ribosomal peptide synthetases and terpene and polyketide cyclases, as well as recent advances of these strategies in an integrated synthesis/biotechnology approach are briefly reviewed.  相似文献   
59.
We show that upon exposure to a remote dc hydrogen plasma, the magnetic and electronic properties of the dilute magnetic semiconductor Ga1-xMnxAs change qualitatively. While the as-grown Ga1-xMnxAs thin films are ferromagnetic at temperatures T less, similar 70 K, the samples are found to be paramagnetic after the hydrogenation, with a Brillouin-type magnetization curve even at T=2 K. Comparing magnetization and electronic transport measurements, we conclude that the density of free holes p is significantly reduced by the plasma process, while the density of Mn magnetic moments does not change.  相似文献   
60.
Boron trifluoride and BBr(3) mediated [2,3]-sigmatropic rearrangements of allylic alpha-amino amides have been developed affording secondary amines in good yields. (E)-Crotyl and (E)-cinnamyl alpha-amino amides 2b and 2c exhibit excellent syn-diastereoselectivity upon rearrangement with either Lewis acid. The allylic amine 2a forms upon treatment with BF(3) or BBr(3) a five-membered heterocylic complex in which a single halide anion has been displaced by the carbonyl oxygen atom. The structures of the Lewis acid-amine complexes were elucidated using NMR spectroscopy. A plausible reaction mechanism, based on DFT calculations, is presented. Thus, BF(3)- or BBr(3)-complexed allylic amines 2 are shown to preferentially proceed, after deprotonation, via an endo transition state.  相似文献   
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