Zur Kenntnis der Zellulosefasern

Zusammenfassung Bei Verwendung gereinigter, hochmolekularer Zellulosen wurde festgestellt, daß die Xanthogenierung in heterogener Phase höchstens bis zu einer-Zahl von 75–80 fortschreitet. Gegenwart überschüssiger flüssiger Phase läßt höhere Xanthogenierungsgrade erhalten.Zellulosen mit einem DP über 1000 sind erst dann zu klaren Viskosen löslich, wenn die-Zahl 50 überschreitet.Der erhaltene höchste Xanthogenierungsgrad ist abhängig vom Abpreßgrad, bzw. der Gegenwart genügender flüssiger Phase. Im Falle der Xanthogenierung in Emulsion genügt bereits eine Alkali-Konzentration von etwa 10%, bei der noch keine Alkali-Zellulose I gebildet wird, um klar lösliche Viskosen zu erhalten.Beim Waschen von Xanthogenaten mit Methanol bzw. Äthanol wird überschüssiges Alkali zurückgehalten. Vergleich der Werte zeigt, daß die Summe der durch Xanthogenierung und durch Alkali besetzten Stellungen des Moleküls etwa mit den erreichbaren-Zahlen übereinstimmen.Bis zu-Zahlen von etwa 75 erfolgt die Xanthogenierung, ohne daß zusätzliche kristalline Bereiche geöffnet werden, also intermizellar.     

Calculated photoelectron spectra of singlet and triplet methylene

Vertical ionization potentials for singlet and triplet methylene are calculated by a CI perturbation method based on ab initio SCF molecular orbitals (6–31 G^** basis). The shape and vibrational fine structure of the first photoelectron band are investigated using the MINDO/3 method. The computed singlet-triplet splitting for methylene is 16.4 kcal/mol, in reasonable agreement with the experimental value of 19.5 kcal/mol.     

Formation of the polycrystalline FeSi phase with the CsCl structure in codeposited thin Fe x Si1 ? x films ( x = 0.5–0.6)

Specific features of the phase formation in the Fe-Si system within the Fe _x Si_{1 − x} (x = 0.5–0.6) concentration range have been investigated. The data obtained by conversion electron M?ssbauer spectroscopy suggest that, for the Fe-Si system in the concentration range x > 0.55, a polycrystalline FeSi phase with the CsCl structure is formed under thermodynamically equilibrium conditions upon annealing at T = 250°C; in this case, the excess (overstoichiometric) Fe atoms are incorporated into the Si sublattice. Previously, the CsCl-FeSi phase was observed only in epitaxially stabilized FeSi/Si(100) layers. Original Russian Text ? A.V. Zenkevich, D.E. Lauer, V.P. Filippov, 2007, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2007, Vol. 71, No. 9, pp. 1313–1315.     

Application of the FAKE molecular-orbital method to diatomic molecules XY (X,Y = H,F, Cl,Br, I)

Theoretical Chemistry Accounts - The FAKE (fast, accurate kinetic energy) method of semiempirical molecular orbital calculation is applied to diatomic molecules XY (X, Y= H, F, Cl, Br, I). The...     

稳态实验考察经模拟道路老化的全配方稀燃Nox捕集催化剂上的Nox还原

Fully formulated lean NOx trap(LNT)catalysts of the type Pt/Rh/BaO/Al2O3 were prepared with and without incorporation of CeO2-ZrO2 in the washcoat,and their NOx reduction behavior was evaluated in steady-state,continuous flow experiments.In the fresh state, the CeO2-ZrO2 addition was found to exert little effect on NOx reduction activity using H2,CO,and NH3 as the reductants.However,after simulated road aging,NOx reduction activity was significantly impaired for the CeO2-ZrO2-free catalyst,whereas the perfo...     

Dual photochemistry of anthracene-9,10-endoperoxide studied by femtosecond spectroscopy

The dual photochemistry of anthracene-9,10-endoperoxide (APO) was investigated in a fs UV pump-supercontinuum probe experiment, along with anthracene (AC) and anthraquinone (AQ) for comparison. Excitation of APO at 282 nm leads to 100% product formation by two competing photoreaction channels. Cycloreversion generates with a ～25% quantum yield (QY) (1)O(2) and AC vibrationally excited in the singlet electronic ground state (hot AC). 1-2% of the AC is generated in the lowest triplet state, but no AC is generated in electronically excited singlet states. Generation and cooling of hot AC are modeled using solution phase and broadened gas-phase AC absorption spectra at various temperatures. Results indicate ultrafast generation of hot AC within 3 ps, much faster than reported before for derivatives of anthracene endoperoxide, and subsequent cooling with an 18 ps time constant. The homolytic O-O cleavage pathway generates a biradical, which converts into electronically excited diepoxide (DE). Our data indicate a 1.5 ps time constant that we tentatively assign to the biradical decay and DE formation. Cooling of DE in this electronically excited state takes place with a ～21 ps time constant. Excitation of AQ at 266 nm is followed by an ultrafast population of the T(1)(nπ*) triplet state of AQ with a time constant of (160 ± 60) fs.     

A search strategy for the elementary cycles of a directed graph

The most successful known algorithms enumerating the elementary cycles of a directed graph are based on a backtracking strategy. Such existing algorithms are discussed and a new backtracking algorithm is proposed which is bounded byO(N +M(C + 1)) time, for a directed graph withN vertices,M edges andC elementary cycles.Research supported by the Conselho National de Desenvolvimento Científico e Tecnológico — CNPq — Brasil.     

First demonstration of “white-light” laser cooling of a stored ion beam

“White-light” cooling of an ion beam confined in a storage ring has been demonstrated at Test Storage Ring in Heidelberg. Measurements aimed at comparing “white-light” with single-mode laser cooling show that “white-light” cooling gives lower temperatures at higher ion densities both in a coasting and in a bunched beam. This revised version was published online in July 2006 with corrections to the Cover Date.