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171.
Significant changes of the hole drift mobility are observed in a-As2Se3 containing concentrations less than ~ 1020 cm?3 of metallic impurities (Mn, Fe, Ni, Cu, Zn, Ga, In, Tl and Na). Depending upon metal concentration the results suggest a modification of the hopping transport channel in Ga, In and Tl doped samples and the buildup of new traps that are either isoenergetic with the intrinsic trap population (Tl, Ga, In, Cu) or lie deeper in the gap (Mn, Fe, Ni, Cu). Trap-limited hopping transport provides a consistent explanation of the experimental data. 相似文献
172.
173.
Helmut Pfister 《Archiv der Mathematik》1975,26(1):646-649
Ohne Zusammenfassung 相似文献
174.
175.
Pfister O Wells JS Hollberg L Zink L Van Baak DA Levenson MD Bosenberg WR 《Optics letters》1997,22(16):1211-1213
We observed cw third-harmonic generation in a periodically poled LiNbO(3) crystal by cascading optimally phase-matched second-harmonic and sum-frequency generation. Other processes, such as fourth-harmonic generation, are allowed by the flexibility of quasi-phase matching. We demonstrate a divide-by-nine (1.19- 10.71-microm) frequency chain that uses only two lasers. 相似文献
176.
Helmut Pfister 《manuscripta mathematica》1977,20(1):51-72
In the first part of this paper we prove the following theorem: Let X be a set, let Y be a separable metrizable uniform space, and let H be any precompact subset of YX; endow X with the coarsest uniformity uH making H uniformly equicontinuous. Then the covering type of (X,uH) equals the weight of H. As a corollary we get: If A is any precompact subset of a locally convex space, then the closed absolutely convex hull
has the same weight as A. In the second part we consider some forms of the closed graph and Banach-Steinhaus theorem depending on some cardinal . Taking =0 will show that the class () of locally convex spaces E introduced by Kalt on [10] can be characterized by the following Banach-Steinhaus condition: If fn, n, and f are linear mappings of E into a separable locally convex space such that each fn is continuous and fn(x)f(x) for every xE, then f is continuous. 相似文献
177.
Methoxybromination of 4,5-dihydro-2-methylfuran ( 4 ), followed by treatment of the resulting bromoketal 5 with hot formamide, gave 4-(2-hydroxyethyl)-5-methyl-1H-imidazole ( 3 ) in 25% yield. This method provides easy access to the selective H2-agonist 4-methylhistamine ( 1 ) via the chloromethyl intermediate 2 . 相似文献
178.
H. Venghaus P. J. Dean P. E. Simmonds J. C. Pfister 《Zeitschrift für Physik B Condensed Matter》1978,30(2):125-128
Excited shallow donor and acceptor states are observed in excitation spectra of donoracceptor pair luminescence in ZnTe. The experiments yield a donor ionization energyE
D =18.3±0.3 meV, and from the Li acceptor 2P
3/2, 2P
5/2(
8), and 2P
5/2(
7) states valence band parametersµ=0.60±0.10 and=0.22±0.05. The latter exceeds values derived from other experiments and indicates considerable nonspherical perturbations associated with this acceptor requiring an extension of existing theories for shallow acceptor states. 相似文献
179.
We derive new inequalities for the plane rotator ferromagnetic model and use them to obtain the following results:
- If the model is isotropic, the derivability of the free energy as function of the magnetic fieldh implies the existence of a unique translation invariant Gibbs state and if furthermoreh=0 all Gibbs states are invariant by rotation of the spins.
- If the model is anisotropic the above assertion holds forh non-zero.
- If the model is anisotropic then there are at most two extremal translation invariant Gibbs states for almost all values of the anisotropy parameter.
180.
Magdalena Pfister Helga Schirmeister Marion Mohr Silke Farkas Klaus-Peter Stengele Tilman Reiner Martin Dunkel Surendra Gokhale Ramamurthy Charubala Wolfgang Pfleiderer 《Helvetica chimica acta》1995,78(7):1705-1737
The 2-(4-nitrophenyl)ethylsulfonyl (npes) group is developed as a new sugar OH-blocking group in the ribonucleoside series. Its cleavage can be performed in a β-eliminating process under aprotic conditions using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as the most effective base. Since sulfonates do not show acyl migration, partial protection of 1,2-cis-diol moieties is possible leading to new types of oligonucleotide building blocks. A series of Markiewicz-protected ribonucleosides 1–10 is converted into their 2′-O-[2-(4-nitrophenyl)ethylsulfonyl] derivatives 29–38 in which the 5′-O? Si bond can be cleaved by acid hydrolysis forming 39–45 . Subsequent monomethoxytritylation leads to 46–50 , and desilylation affords the 5′-O-(monomethoxytrityl)-2′-O-[2-(4-nitrophenyl)ethylsulfonyl]ribonucleosides 51–55 . Acid treatment to remove trityl groups do also not harm the npes group (→ 56–58 ). Unambiguous syntheses of fully blocked 2′-O-[2-(4-nitrophenyl)ethylsulfonyl]ribonucleosides 96–102 are achieved from the corresponding 3′-O-(tert-butyl)dimethylsilyl derivatives. Furthermore, various base-protected 5′-O-(monomethoxytrityl)- and 5′-O-(dimethoxytrityl)ribonucleosides, i.e. 59–77 , are treated directly with 2-(4-nitrophenyl)ethylsulfonyl chloride forming in all cases a mixture of the 2′,3′-di-O- and the two possible 2′- and 3′-O-monosulfonates 107–148 which can be separated into the pure components by chromatographic methods. The npes group is more labile towards DBU cleavage than the corresponding base-protecting 2-(4-nitrophenyl)ethyl (npe) and 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) groups allowing selective deblocking which is of great synthetic potential. 相似文献