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排序方式: 共有548条查询结果,搜索用时 15 毫秒
71.
Blanca Rojas de Gáscue José Luis Prin Gilma Hernández Enrique M. Vallés Arnaldo T. Lorenzo Alejandro J. Müller 《Journal of Thermal Analysis and Calorimetry》2011,103(2):669-678
The application of the Successive Self-nucleation and Annealing (SSA) thermal fractionation technique can yield detailed information
of the structural changes induced in linear polyethylene by irradiation. The production of tertiary carbons during the crosslinking
reactions can be equivalent to the structural heterogeneity present in branched polyethylenes since in both cases interruption
of the linear crystallizable sequences occurs, and these are structural differences that can be easily detected by thermal
fractionation. We demonstrate how correlations between melting point and short chain branching content employed for branched
polymers can be useful to characterize the distribution of chain heterogeneity produced by crosslinking. As the radiation
dose is increased and the crosslinking content also increases, the distribution of chain heterogeneity gets broader as detected
by SSA. When the results are coupled with morphological observations made by transmission electron microscopy, valuable information
on the morphological changes produced by crosslinking can also be ascertained, since the distribution of lamellar thicknesses
substantially broadens with crosslinking. Such a broad distribution can also be predicted from SSA by simple calculations
performed employing a modified version of the Gibbs–Thomson equation and is expected on the basis of random crosslinking reactions. 相似文献
72.
Foundations of Computational Mathematics - We show that there exist real parameters $$c\in (-2,0)$$ for which the Julia set $$J_{c}$$ of the quadratic map $$z^{2} + c$$ has arbitrarily high... 相似文献
73.
Y. Rojas Martínez G. A. Pérez Alcázar H. Bustos Rodríguez D. Oyola Lozano 《Hyperfine Interactions》2005,161(1-4):191-195
In this work we report a comparative study of the magnetic and structural properties of Fe50Al50 alloys produced by mechanical alloying using two different planetary ball mills with the same ball mass to powder mass relation.
The Fe50Al50 sample milled during 48 h using the Fritsch planetary ball mill pulverisette 5 and balls of 20 mm, presents only a bcc alloy
phase with a majority of paramagnetic sites, whereas that sample milled during the same time using the Fritsch planetary ball
mill pulverisette 7 with balls of 15 mm, presents a bcc alloy phase with paramagnetic site (doublet) and a majority of ferromagnetic
sites which include pure Fe. However for 72 h of milling this sample presents a bcc paramagnetic phase, very similar to that
prepared with the first system during 48 h. These results show that the conditions used in the first ball mill equipment make
more efficient the milling process. 相似文献
74.
We calculate the hadronic width (damping rate) of pions and nucleons at finite temperature in the framework of the linear sigma model, and to lowest order in the virial expansion. Results indicate a substantial growth of both widths even at moderately low temperatures. 相似文献
75.
Deanna De Marcano Bernardo Mndez Jeannette De Mndez Jos Monasterios Aníbal C. Rojas Thomas G. Halsall 《Magnetic resonance in chemistry : MRC》1983,21(8):524-525
The 13C NMR spectra of a series of some Δ4(20),11-taxadiene derivatives are reported. A detailed analysis of their assignments is presented. 相似文献
76.
N. Gañán Gutiérrez F. Sánchez Rojas J. M. Cano Pavón 《Fresenius' Journal of Analytical Chemistry》1996,355(1):88-91
A room-temperature flow injection spectrofluorimetric method is presented for the determination of Zn(II), based on the use of salicylaldehyde thiocarbohydrazone in the presence of Triton X-100 and sodium acetate-acetic acid buffer. Various physical and chemical variables affecting the reaction in the flow system were evaluated. The proposed method is very selective. The calibration graph is linear over the range 10–1000 ng/ml, with a detection limit of 5 ng/ml and a relative standard deviation at the 50 ng/ml level of 1.8 %. The method was successfully applied to the determination of Zn(II) in drinking waters and biological samples. 相似文献
77.
CM Thaker S Rayaprol Krushna Mavani DS Rana MS Sahasrabudhe SI Patil DG Kuberkar 《Pramana》2002,58(5-6):1035-1039
The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO3 perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good
example of these properties is (La1−2x
Pr
x
Ca
x
)MnO3 (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T
c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using
X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for
understanding the structural, transport and magnetic properties are discussed in detail. 相似文献
78.
The title compounds 1b and 1c were synthesized from manool. On treatment with either trifluoroacetic acid or formic acid 1b provided in nearly 100% yield 4a with a rearranged labdane skeleton. With sulfuric acid, however, 1b gave solely Δ8,9-isomer 5. Reduction of 4a with lithium diisobutylaluminum hydride afforded 4b. On treatment with sulfuric acid 4a reverted to 5. Rearrangement of the epoxide 6 with boron trifluoride- etherate led to a complex product mixture from which no pure substance was obtained. 相似文献
79.
We study the nonradiative processes in diatomic molecules produced by a potential surface crossing in terms of a generalized optical potential containing an absorptive and a resonant part. The theory is applicable to inelastic atomic scattering, predissociation, accidental predissociation and collisionally induced dissociation. The coupling term between the electronic surfaces (in the diabatic representation) is evaluated semiclassically in terms of the “inelastic action” s. While the Landau–Zener formula is obtained from a linearized function of s, a more realistic form is proposed as a rational fraction in s. 相似文献
80.
Summary A kinetic method for determination of traces of Ce(IV), based on the oxidation of sodium 4,8-diamino-1,5-dihydroxyanthraquinone-2, 6-disulphonate is described. The reaction is monitored by means of the fluorescence of the oxidation product (
ex=525nm,
em=585 nm), and allows determination of 0.02–0.37 ppm Ce(IV). The proposed method has few interferences.
Kinetisch-fluorimetrische Bestimmung von Mikromengen Cer(IV) mit Natnum-4,8-diamino-1,5-dihydroxyanthrachinon-2,6-disulfonat
Zusammenfassung Eine kinetische Methode zur Bestimmung von Spuren Cer(IV) mit Hilfe von Natrium-4,8-diamino-1,5-dihydroxyanthrachinon-2,6-disulfonat wurde beschrieben. Dabei wird ein fluoreszierendes Oxydationsprodukt gebildet, das bei 525 nm angeregt mit einer maximalen Emission bei 585 nm fluoresziert. Die Reaktion ermöglicht die Bestimmung von 0,02–0,37 ppm Cer(IV). Die vorgeschlagene Methode wird nur durch wenige Störungen eingeschränkt.相似文献