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71.
Alcohol ethoxylates (AEs) are nonionic surfactants. They are industrially important compounds that have historically been difficult to analyze, with the best results to date achieved through derivatization (e.g., silylation) followed by analysis by gas chromatography/mass spectrometry (GC/MS). Recently, mass spectrometric techniques such as field desorption (FD), time-of-flight secondary ion mass spectrometry (TOF-SIMS), fast atom bombardment (FAB), electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) have been employed to analyze surfynol(R) 4xx. In an effort to produce low-cost alkyl-capped AEs and anionic detergents from AEs, a fast and reliable measure of the product yields and conversions from AEs is required in research. We found that the product yields and conversions from reactions of AEs, obtained by the employment of atmospheric pressure chemical ionization (APCI), were in good agreement with those obtained from proton nuclear magnetic resonance spectroscopy ((1)H-NMR). Therefore, APCI can be used as a validated tool for studying AE reactions. Mixtures that contain either silylated or unsilylated ethoxylates and/or carboxylates yield the same APCI mass spectra. Copyright -Copyright 1999 John Wiley & Sons, Ltd. 相似文献
72.
Ki Hwan Bae 《中国化学快报》2009,20(11):1321-1323
Phytochemical study on the BuOH-soluble fraction of the stem bark of Populus davidiana resulted in the isolation of a new salicin derivative(1),named davidianoside.The structure was elucidated on the basis of extensive physicochemical and spectroscopic analyses. 相似文献
73.
A. L. Rakhmanov K. I. Kugel M. Yu. Kagan A. V. Rozhkov A. O. Sboychakov 《JETP Letters》2017,105(12):806-817
A brief overview of the theoretical studies on the electronic phase separation in the systems with the imperfect nesting of Fermi surface sheets is presented. Among these systems, there are chromium and its alloys, superconducting iron-based pnictides, bilayer graphene, and some other materials. 相似文献
74.
K. I. Kugel L. G. Mamsurova K. S. Pigalskiy A. L. Rakhmanov 《Physica C: Superconductivity and its Applications》1998,300(3-4):270-280
The nature of hysteretic behavior of the flux line lattice (FLL) contribution to ac magnetic permeability (μv) is analyzed for the case of YBa2Cu3Ox single crystal (at applied magnetic field Hc axis). It is shown that hysteresis loops μv(H) corresponding to different temperatures (T=70–84 K) are scaled to a universal curve in normalized coordinates. Such a behavior is interpreted in terms of the FLL interaction with the crystal surface. The explicit relationship between μv and magnetic induction B is found for the near-surface region of the superconductor. It is shown that the μv(H) loops are closely related to the hysteresis of B at cycling of applied magnetic field. The latter hysteresis stems from the Bean–Livingston surface barrier. The estimates demonstrate strong suppression of the surface barrier in YBa2Cu3Ox crystal in comparison to that expected for the ideal surface. As a result, the lower branch of the hysteresis loop corresponding to the increasing field is very close to the equilibrium μv(H) curve and the surface barrier appreciably affects only the upper branch when magnetic flux leaves the sample. The comparison of theoretical predictions and experimental data provides an opportunity to refine the actual range of stability Hmax(B)–Hmin(B) for the FLL at fixed B for YBa2Cu3Ox crystal in the case of Hc. 相似文献
75.
S Rayaprol Krushna Mavani CM Thaker DS Rana Keka Chakravorty SK Paranjape M Ramanadham Nilesh A Kulkarni DG Kuberkar 《Pramana》2002,58(5-6):877-880
A new series of mixed oxide superconductors with the stoichiometric composition La2−x
Dy
x
Ca
y
Ba2Cu4+y
O
z
(x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La2−x
(Y/Er)
x
Ca
y
Ba2Cu4+y
O
z
series, show a strong dependence of T
c on hole concentration (p
sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant
displacement of La onto Ba site. Superconductivity studies show that maximum T
c is obtained for x=0.5, y=1.0 sample (T
c ∼ 75 K), for La1.5Dy0.5Ca1Ba2Cu5O
z
(La-2125). 相似文献
76.
S. E. Kichanov E. V. Frolova G. P. Shevchenko D. P. Kozlenko A. V. Belushkin E. V. Lukin G. E. Malashkevich S. K. Rakhmanov V. P. Glazkov B. N. Savenko 《Physics of the Solid State》2013,55(4):813-820
The specific features of the crystal structure of crystal phosphors Y3Al5O12: Ce3+/Lu2O3 (Lu2O3: Ce) synthesized by the colloidal chemical method have been investigated by neutron diffraction at room temperature. The influence of the method used for introducing Lu2O3 into the system on the structure and luminescence properties of the samples has been analyzed. The investigation has revealed that the spectra of the samples prepared under the most nonequilibrium conditions are characterized by the Stokes shift and high photoluminescence intensity. This has been explained by the disorder of their crystal structure due to the formation of stable associates of defects. 相似文献
77.
The magnetooptical method was used to investigate the penetration of a magnetic flux into a single crystal of a high-temperature superconductor (Bi0.84Pb0.16)2.2Sr2CaCu2O8 in crossed magnetic fields. It is shown that at low temperatures the penetration of the magnetic flux is anisotropic: the flux moves preferentially along the magnetic field applied in the plane of the sample, and the anisotropy grows as the temperature increases. At a temperature Tm = 54±2 K, there occurs a sharp change in the character of penetration of the magnetic field into the superconductor; the direction of the flux ceases be dependent on the direction and magnitude of the magnetic field applied in the plane of the sample. In this case, the transition temperature Tm is independent of the applied magnetic field. The effect is interpreted in terms of the concepts of a phase transition in the system of vortices, which is related to a sharp decrease in the correlations in the position of vortices in various CuO planes, i.e., with the transition from three-dimensional to two-dimensional behavior of the vortex structure. 相似文献
78.
B. N. Rakhmanov 《Mathematical Notes》1978,23(4):324-328
We are considering a class S of functions F(z), F(0) = 0, F′(0) = 1 that are univalent and regular in the circle ¦z¦ < 1, and its subclasses s h * and K of starlike functions of order h and of convex functions respectively. Among others, we establish the following results: If F(z)εs and 0 < α < 1, then IfF (z) ε s (0 < a < 1) and $$\begin{gathered} 1 + \operatorname{Re} {{z_1 F^n \left( {z_1 } \right)} \mathord{\left/ {\vphantom {{z_1 F^n \left( {z_1 } \right)} {F'\left( {z_1 } \right)}}} \right. \kern-\nulldelimiterspace} {F'\left( {z_1 } \right)}} = \operatorname{Re} {{\alpha z_1 F''\left( {\alpha z_1 } \right)} \mathord{\left/ {\vphantom {{\alpha z_1 F''\left( {\alpha z_1 } \right)} {F'\left( {\alpha z_1 } \right)}}} \right. \kern-\nulldelimiterspace} {F'\left( {\alpha z_1 } \right)}} \hfill \\ \left( {2 - \sqrt 3< \left| {z_1 } \right| = r< 1} \right) \hfill \\ \end{gathered} $$ then we obtain the domain of values of the point αz1. 相似文献
79.
New functionalized dithia-12(13)-crown-4 ethers: Synthesis,complex formation,and extraction capacity
A. A. Zenina E. V. Rakhmanov A. A. Bobyleva E. V. Lukovskaya L. G. Kuzmina A. A. Abramov A. V. Anisimov 《Chemistry of Heterocyclic Compounds》2007,43(7):835-843
1,4-Dioxa-7,10-dithiacyclododecane-8-carbonitrile, 1,4-dioxa-7,11-dithiacyclotridecan-9-one, its 2,4-dinitrophenylhydrazone,
and unsubstituted 7,10-dithia-12-crown-4 were synthesized. The complexing ability of the four synthesized dioxadithiacrown
compounds toward Ag(I), Pb(II), Hg(II), and Cd(II) ions was assessed by 1H NMR. The extracting ability of the three dioxadithiacrown compounds with respect to the Sn(II) ion from aqueous solutions
was studied. The thermal stability of 1,4-dioxa-7,10-dithia-cyclododecane and the corresponding 8-carbonitrile was investigated.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 992–1000, July, 2007. 相似文献
80.
We investigate two problems concerning uniform approximation by weighted rationals {w nrn~ ∞ n=1 }, wherer n=pn Namely, forw(x):=e x we prove that uniform convergence to 1 ofw nrn is not possible on any interval [0,a] witha>2π. Forw(x):=x ?, ?>1, we show that uniform convergence to 1 ofw nrn is not possible on any interval [b, 1] withb<tan 4(π(??1)/4?). (The latter result can be interpreted as a rational analogue of results concerning “incomplete polynomials.”) More generally, for α≥0, β≥0, α+β>0, we investigate forw(x)=e x andw(x)=x ?, the possibility of approximation byw n pn/qn~ ∞ n=1 , where depp n≤αn, degq n≤βn. The analysis utilizes potential theoretic methods. These are essentially sharp results though this will not be established in this paper. 相似文献