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991.
J. Telser H. -I. Lee E. T. Smith H. Huang P. Brereton M. W. W. Adams R. C. Conover M. K. Johnson B. M. Hoffman 《Applied magnetic resonance》1998,14(2-3):305-321
The hyperthermophilic archaeonPyrococcus furiosus contains a four-Fe ferredoxin (Pf- Fd) that differs from most other 4Fe-Fd’s in that its [Fe4S4] cluster is anchored to protein by only three cysteinyl residues.Pf- Fd also is of interest because in its reduced form, [Fe4S4]+, the cluster exhibits bothS = 1/2 andS = 3/2 spin states. Addition of excess cyanide ion converts the cluster exclusively to anS = 1/2 state (g1 = 2.09, g2 = 1.95, g3 = 1.92), however dialysis restores the EPR signal of native reduced protein indicating that the cluster is not irreversibly altered by cyanide. Both the native protein and protein in the presence of excess cyanide ion (Pf- Fd 4Fe-CN) were investigated here using the techniques of electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy. In particular,Pf- Fd 4Fe-CN was investigated using13CN? and C15N? ligands.13C and15N ENDOR indicated that a single cyanide ion bound directly, with the cluster showing an unusually small contact interaction (aiso(13C)~ ?3 MHz, aiso(15N) ~ 0). This is in contrast to cyanide bound to monomeric low-spin Fe(III)-containing proteins such as transferrin and myoglobin, for which the13C hyperfine coupling has a large isotropic component (aiso(13C) ≈ ?30 MHz). This small contact interaction is not due to low spin density of Fe, as57Fe ENDOR of the singly and triply labeledPf- Fd 4FeCN isotopologs, [57FeFe3S4]+ and [Fe57Fe3S4]+, show hyperfine coupling characteristic for [Fe4S4]+ clusters, particularly for the Fe to which cyanide binds. Thus, the low spin density on13C is not due to low spin density on the Fe ion to which it binds. Further theoretical work is needed to explain the contrast between the strong electronic effect of cyanide ion binding with the low spin density on the ligand. 相似文献
992.
D. T. Satybaldyeva M. Yu. Mukhamedzhanova A. A. Sarymsakov Yu. T. Tashpulatov 《Chemistry of Natural Compounds》1998,34(3):322-325
The results are given of a study of the rheological properties of concentrated solutions of CNC and agar-agar and the influence of their quantitative ratio on the anomalous flow behavior of their solutions. A hypothesis is put forward of the formation of intermolecular associates from CMC and agar-agar which leads to the formation of a stronger structural network of solutions of the initial polysaccharides.Institute of the Physics and Chemistry of Polymers, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (371) 1 44 26 61. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 357–361, May–June, 1998. 相似文献
993.
Let F denote a family of pairwise disjoint convex sets in the plane. F is said to be in convex position if none of its members is contained in the convex hull of the union of the others. For any fixed k≥ 3 , we estimate P
k
(n) , the maximum size of a family F with the property that any k members of F are in convex position, but no n are. In particular, for k=3 , we improve the triply exponential upper bound of T. Bisztriczky and G. Fejes Tóth by showing that P
3
(n) < 16
n
.
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<onlinepub>26 June, 1998
<editor>Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt;
<pdfname>19n3p437.pdf
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Received March 27, 1997, and in revised form July 10, 1997. 相似文献
994.
T. A. Zhakatakev 《Journal of Applied Mechanics and Technical Physics》1993,34(4):535-537
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 4, pp. 97–99, July–August, 1993. 相似文献
995.
I. S. Kim N. L. Krussanova I. V. Alekseeva R. N. Smartt 《Radiophysics and Quantum Electronics》1998,41(2):94-98
A new approach to investigating the statistical relationship between certain solar features and recurrent wind streams is
presented. This approach is based, on a comparative analysis of the distributions of lifetimes of a set of solar features,
recurrent geomagnetic disturbances, and geomagnetic “calms.” Correlation coefficients of 0.81, 0.85, 0.79, and 0.77 are found
for the distributions of several solar features—filaments, large-scale magnetic fields, coronal features, and coronal holes,
respectively—and recurrent geomagnetic disturbances. A correlation factor of 0.97 between the distributions of geomagnetic
“calms” and active regions is found. The combined evidence indicates that no specific type of solar feature is responsible
for the recurrent stream activity. Rather, the configuration of the large-scale magnetic field of the Sun appears to control
the permanently existing corpuscular activity. Since prominences trace polarity division lines of the large-scale magnetic
field structure of the Sun, they have been checked as a possible general predictor of recurrent corpuscular activity; their
parameters could present the most reliable indices that relate closely with trends in geomagnetic disturbances. A comparative
analysis of cyclic variations of sunspot numbers, the total number of prominences, the relative number of low-height (<-20″)
prominences, and recurrent geomagnetic storms is made for solar cycle N16. The relative number of low-height prominences is
found to correlate broadly (0.83) with recurrent wind streams.
P. K. Shternberg State Astronomical Institute, Moscow, Russia; National Solar Observatory, Sacramento Peak, U.S. Published
in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 2, pp. 145–151, February, 1998. 相似文献
996.
We present an asymptotic analysis of the boundary-generated, small-amplitude, high-frequency waves in a one-dimensional, semi-infinite, viscoelastic solid characterized by a single-integral constitutive functional. The equations governing the wave motion constitute a 2×2 system of hyperbolic Volterra integrodifferential equations. The method of analysis is based on a single-wave expansion of nonlinear geometric optics. 相似文献
997.
In connection with a characteristic feature of the effective optical potential in the Dirac approach two types of time delays are considered in the relativistic eikonal approximation. One is obtained from the scattering amplitude and the other given by the wave packet motion in the interaction region. These time delays turn out to differ in sign at intermediate energies, in contrast to the agreement between corresponding nonrelativistic time delays. 相似文献
998.
In this paper we study a method for the approximation by a monotone smooth function of a discrete set of observations. By this method it is possible to obtain a completely automatic program. We show that the solution is monotone with probability tending to one and by the test examples that it is sufficient in the practical case.This work was supported by the Italian M.U.R.S.T. 相似文献
999.
This paper significantly extends and generalizes the paragrassmann calculus of our previous paper [1]. Here we discuss explicit general constructions for paragrassmann calculus with one and many variables. For one variable, nondegenerate differentiation algebras are identified and shown to be equivalent to the algebra of (p+1)×(p+1) complex matrices. If (p+1) is a prime integer, the algebra is nondegenerate and so unique. We then give a general construction of many-variable diffeentiation algebras. Some particular examples are related to multi-parametric quantum deformations of the harmonic oscillators.Dedication This paper is in memory of Mikhail Constantinovich Polivanov. One of the authors (A.T.F.) had a privilege to be a friend of him for many and many years. He was not only a distinguished scientist but a true Russian intellectual having deep roots in Russian culture. It is a deep sorrow that we can no more have a talk with him on science, poetry, religion ...Laboratory of Theoretical Physics, JINR, Dubna. SU-101 000 Moscow, Russia. Published in Teoreticheskaya i Matematicheskaya Fizika, Vol. 94, No. 2, pp. 213–231, February, 1993. 相似文献
1000.
A. I. Golovashkin N. V. Anshukova L. I. Ivanova O. T. Maljuchkov A. P. Rusakov 《Czechoslovak Journal of Physics》1996,46(3):1191-1192
On the basis of new experimental studies of specific heat, magnetic properties and thermal expansion, it was shown that dielectric-metal phase transitions were the consequence of delocalization of the heavy holes located on metalapical oxygen bonds in the high-Tc oxide systems. The ordered arrays of such holes (CDW) results in the dielectric gaps in electron spectrum and anomalous negative thermal expansion. The free carriers introduced by doping can couple through excitations of these localized holes, (local bosons). The high-Tc superconductivity will possess anomalous Hc2(T) dependence and γ-type specific heat jump at Tc. This local bosons model is the basis for explanation of the obtained experimental data. 相似文献