On nonnegative solvability of linear operator equations

LetE be a Banach lattice having order continuous norm. Suppose, moreover,T is a nonnegative reducible operator having a compact iterate and which mapsE into itself. The purpose of this work is to extend the previous results of the authors, concerning nonnegative solvability of (kernel) operator equations on generalL ^p-spaces. In particular, we provide necessary and sufficient conditions for the operator equation x=T x+y to possess a nonnegative solutionxE wherey is a given nonnegative and nontrivial element ofE and is any given positive parameter.     

Eclipsed Isopropyl Conformations of Two Dimeric Hydrazines

The X-ray structures of 4,10-di-tert-butyl-5,9-diisopropyl-4,5,9,10-tetraazatetracyclo[6.2.2.2(3,6)]tetradecane (s4iPr) and its 4,9-di-tert-butyl-5,10-diisopropyl isomer (a4iPr) are reported. Both compounds are in conformations having their in-N-alkyl groups (directed toward the central CH-CH bond of the molecule) anti to each other, as expected from previous work. The principal feature of interest is that one in-isopropyl group in each compound is in an eclipsed conformation, NN,C(alpha)Me twist angle -0.5(5) degrees for s4iPr and -6.4(4) degrees for a4iPr. Low energy (somewhat less) eclipsed in-isopropyl conformations are predicted by both molecular mechanics (MM2) and semiempirical quantum mechanical (AM1) calculations. The asymmetry of the potentially C(2) symmetric a4iPr because the two in-isopropyl groups are in different rotamers is apparently not a result of crystal packing forces, because a conformation with different isopropyl rotamers is the more stable one by at least 1.0 kcal/mol in solution, determined by (13)C-NMR spectroscopy. This result is not predicted by either calculation method. The "monomer", 2-tert-butyl-3-isopropyl-2,3-diazabicyclo[2.2.2]octane (3), proves to be a poor model for the conformations of 4iPr.     

Quantum-chaotic scattering effects in semiconductor microstructures

We show that classical chaotic scattering has experimentally measurable consequences for the quantum conductance of semiconductor microstructures. These include the existence of conductance fluctuations-a sensitivity of the conductance to either Fermi energy or magnetic field-and weak-localization-a change in the average conductance upon applying a magnetic field. We develop a semiclassical theory and present numerical results for these two effects in which we model the microstructures by billiards attached to leads. We find that the difference between chaotic and regular classical scattering produces a qualitative difference in the fluctuation spectrum and weak-localization lineshape of chaotic and nonchaotic structures. While the semiclassical theory within the diagonal approximation accounts well for the weak-localization lineshape and for the spectrum of the fluctuations, we uncover a surprising failure of the semiclassical diagonal-approximation theory in describing the magnitude of these quantum transport effects.     

Determination of lead in petroleum and petroleum products by atomic absorption spectrometry with a carbon rod atomizer

The use of a carbon rod atomizer for the analysis of lead in petroleum and petroleum products is described. Variables affecting sensitivity studied include: type of lead salt and type of solvent for standard and sample preparation, hydrogen diffusion flame, choice of analytical wavelength and interferences. For the 217.00-nm line, a sensitivity of 1·10^-11 g (absolute) and for the 283.31-nm line, a detection limit of 2·10^-12 g (absolute) are reported. Results of analysis of gasoline, used bunker heating oil, used jet engine lubricating oil, and crude oil for lead content are presented. An organic-to-aqueous solvent extraction system for lead is described.     

Spectroscopic investigations in molecularly organized solvent media. Part 3. Examination of the nitromethane selective quenching rule in aqueous anionic + cationic and anionic + nonionic mixed surfactant solutions

Applicability of the nitromethane selective quenching rule for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is examined for 20 representative PAH solutes dissolved in micellar sodium dodecylsulfate (SDS) + cetyltrimethylammonium bromide (CTAB), SDS + dodecyltrimethylammonium bromide (DTAB), SDS + Brij-35, and SDS + sodium octanoate (SO) mixed surfactant solvent media. Experimental results show that nitromethane quenched fluorescence of all 8 alternant PAHs studied in the four different solvent systems. Unexpected quenching behavior was observed, however, in the case of nonalternant PAHs. Nitromethane quenched fluorescence emission of nonalternant PAHs dissolved in the SDS + SO solvent media, which is contrary to the selective quenching rule. In the case of the mixed anionic + cationic surfactant solvent media, nitromethane quenching selectivity was restored at concentration ratios of approximately 4 : 1 (anionic:cationic) or less. Received: 22 May 1997 / Revised: 29 September 1997 / Accepted: 3 October 1997     

Die elektrische Zerstäubung von Silicium in Aceton

Zusammenfassung Die Bildung kolloider L?sungen durch Hochspannungskurzschlu\funken zwischen kleinen Siliciumstücken in Aceton unter sauerstoffreiem Stickstoff wird untersucht: sowohl die Ver?nderungen der Siliciumoberfl?chen durch das kurzzeitige Schmelzen und Verdampfen des Siliciums, als auch die chemischen Eigenschaften der in L?sung befindlichen Kolloide. Das Interesse war nicht, wie bei der Svedbergschen Kolloidzerst?ubung, auf die Methode zur Herstellung kolloider Metalle, in diesem Falle kolloiden Siliciums, gerichtet, sondern auf die chemische Umsetzung des Siliciums unter den gegebenen extremen Temperaturbedingungen mit dem Aceton zu kolloiden Siliciumverbindungen. Durch fraktioniertes Zentrifugieren und Eindampfen der Restl?sung ist die kolloide L?sung der Siliciumverbindungen in 3 Anteile zerlegt worden: Ein braunes Pulver, schwarze Flocken und ein dem Silikagel ?hnliches Gel. Die 3 Substanzen enthielten alle Si, O, C und H in Form einer anorganischen Si-O-haltigen Komponente und einer unges?ttigten Kohlenwasserstoffkomponente. Je gr?\er der Anteil der organischen Komponente ist, desto kleiner und l?slicher sind die Kolloidteilchen in Aceton. Die Struktur der Gelteilchen ist sehr labil und geht unter Verglimmen in eine stabilere aber nicht kristalline über. Dieser Vorgang findet beim Erw?rmen, auch unter vollkommenem Ausschlu\ von Sauerstoff, statt. Das Gel l?st sich in Laugen und flockt wieder mit S?uren. Das ganze Verhalten, einschlie\lich der analytischen Befunde, l?\t darauf schlie\en, da\ die hier erhaltene kolloide L?sung, aber auch das Svedbergsche Siliciumsol nicht kolloides elementares Silicium enthalten, sondern Kolloidteilchen, die silikonharzartigen Charakter besitzen. Hans Kautsky Jun. Diss. (Marburg 1954). Mein Vater, Prof. Dr. Hans Kautsky, regte mich zu dieser Arbeit an und gab mir wertvolle Ratschl?ge; ich danke ihm herzlich dafür. Herrn Dr. E. Hellner vom mineralogischen Institut der Philipps-Universit?t Marburg/Lahn, der die R?ntgenuntersuchungen unserer Substanzen vorgenommen hat, sei an dieser Stelle auch vielmals gedankt. Zu besonderem Dank bin ich der Deutschen Forschungsgemeinschaft für die apparative Unterstützung der Arbeit verpflichtet, der Firma Rosenthal-Isolatoren Gesellschaft m. b. H., Selb, für die kostenlose überlassung der Kondensatorbatterie.     

Thermochemical properties of benzoic acid derivatives VIII. Enthalpies of combustion and formation of o-, m-, and p- t-butylbenzoic acids

The enthalpies of formation in the crystalline state at 298.15 K of o-, m-, and p-t-butyl-benzoic acids have been determined by static-bomb calorimetry. Vapour-pressure determinations were made by the Knudsen-effusion technique and the sublimation enthalpies at the mean temperatures of the measurement ranges have been derived for the three acids. The values obtained are:

     

30.

Chemical modification of a viral cage for multivalent presentation     

Gillitzer E  Willits D  Young M  Douglas T 《Chemical communications (Cambridge, England)》2002,(20):2390-2391

Here we present generalized methods for chemically modifying the surface of a viral protein cage; this exploits the chemistry of native and engineered surface exposed functional groups for multivalent presentation of ligands.     

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	$\text{ΔH}{}_{\mathrm{f}}{}^{\mathrm{o}}\text{(c, 298.15 K)/kJ mol}{}^{\mathrm{?1}}$	$\text{ΔH}{}_{\mathrm{s}}\text{/kJ mol}{}^{\mathrm{?1}}$
o-t-butylbenzoic acid	476.2 ± 1.9	99.8 ± 0.4	(at 314.6 K)
m-t-butylbenzoic acid	504.3 ± 1.6	103.0 ± 0.5	(at 326.5 K)
p-t-butylbenzoic acid	502.9 ± 1.7	103.8 ± 0.4	(at 334.1 K)

Chemical modification of a viral cage for multivalent presentation

Here we present generalized methods for chemically modifying the surface of a viral protein cage; this exploits the chemistry of native and engineered surface exposed functional groups for multivalent presentation of ligands.