Collocation Methods for Weakly Singular Second-kind Volterra Integral Equations with Non-smooth Solution

Collocation type methods are studied for the numerical solutionof the weakly singular Volterra integral equation of the secondkind: where the solution (t) is assumedto have the form f(t) = x(t)+r^?(t), x and being sufficientlysmooth. The solution is approximated near zero by a linear combinationof powers of t?, and away from zero by the usual polynomialrepresentation. Convergence is proved and many numerical experimentsare carried out with examples from the literature. A comparisonis made with a method of Brunner & Norsett (1981), originallydeveloped for (1) with a smooth solution. Special attentionis paid to the numerical approximation of the so-called momentintegrals which emerge in the collocation scheme.     

Thermodynamic properties of CeCu6-xAux: Fermi-liquid vs. non-Fermi-liquid behaviour

We report on a detailed comparison of the thermodynamic properties of the heavy-fermion system CeCu₆ which can be described as a Fermi liquid at low temperatures T < 0.1 K, and CeCu_5.9Au_0.1 where strong deviations from the Fermi-liquid behaviour were found previously in the T dependence of the specific heat C, magnetization M and electrical resistivity p. The specific heat, magnetization and elastic constants are investigated in a large range of magnetic fields, corroborating the idea that the non-Fermi-liquid behaviour arises from low-lying spin excitations. For the elastic constants, a striking linear T dependence is found for CeCu_5.9Au_0.1 in contrast to the T² Fermi-liquid behaviour of CeCu₆.     

Metals near a magnetic instability

Zero-temperature magnetic phase transitions exhibit an abundance of nearly critical magnetic fluctuations that allow to probe the traditional concepts of the metallic state. For the prototypical heavy-fermion compound, CeCu_6−x Au _x , a breakdown of the Fermi-liquid properties may be tuned by Au concentration, hydrostatic pressure, or magnetic field. The d-electron weak itinerant ferromagnet ZrZn₂, on the other hand, was recently found to display superconductivity in coexistence with ferromagnetism.     

无机酸洗脱对胜利褐煤微晶结构及其自燃倾向性的影响

利用XRD、Raman、XPS和FT-IR表征技术,研究无机酸洗脱(HCl、H2SO4、HCl-HF)处理的胜利褐煤微晶结构的变化,采用自行设计的表面吸附仪-GC联用装置,对样品进行不同温度的低温脉冲氧化实验,考察了煤样在不同温度下氧吸附量的变化规律,通过低温脉冲氧吸附规律与TG/DTG和固定床燃烧实验关联,考察了煤样的自燃倾向。结果表明,无机酸洗脱对矿物质的脱除使得煤结构的有序度增加,石墨化程度提高,无机酸洗脱煤样与原煤相比吸氧量明显下降。随着吸附温度的升高,各煤样吸氧量明显增加,且随着脱除矿物质程度的增加,吸氧量呈减小的趋势,导致自燃倾向降低。     

An approximate treatment of scattering based on the delta boundary operator

The development of a scheme to treat two-dimensional electromagneticscattering by electrically large, perfectly conducting bodiesis described. It incorporates the effects of surface curvatureand non-local phenomena and has the potential to provide thebasis for a general technique yielding more accurate predictionsthan the widely used physical optics method.     

Quantum criticality in the cubic heavy-fermion system CeIn3-xSnx

We report a comprehensive study of CeIn3-xSnx (0.55相似文献   

Elucidation of the function of two glycosyltransferase genes (lanGT1 and lanGT4) involved in landomycin biosynthesis and generation of new oligosaccharide antibiotics

BACKGROUND: The genetic engineering of antibiotic-producing Streptomyces strains is an approach that became a successful methodology in developing new natural polyketide derivatives. Glycosyltransferases are important biosynthetic enzymes that link sugar moieties to aglycones, which often derive from polyketides. Biological activity is frequently generated along with this process. Here we report the use of glycosyltransferase genes isolated from the landomycin biosynthetic gene cluster to create hybrid landomycin/urdamycin oligosaccharide antibiotics. RESULTS: Production of several novel urdamycin derivatives by a mutant of Streptomyces fradiae Tü2717 has been achieved in a combinatorial biosynthetic approach using glycosyltransferase genes from the landomycin producer Streptomyces cyanogenus S136. For the generation of gene cassettes useful for combinatorial biosynthesis experiments new vectors named pMUNI, pMUNII and pMUNIII were constructed. These vectors facilitate the construction of gene combinations taking advantage of the compatible MunI and EcoRI restriction sites. CONCLUSIONS: The high-yielding production of novel oligosaccharide antibiotics using glycosyltransferase gene cassettes generated in a very convenient way proves that glycosyltransferases can be flexible towards the alcohol substrate. In addition, our results indicate that LanGT1 from S. cyanogenus S136 is a D-olivosyltransferase, whereas LanGT4 is a L-rhodinosyltransferase.     

Nature of the A phase in CeCu2Si2

Neutron diffraction experiments have been performed on a magnetically ordered CeCu2Si2 single crystal exhibiting A-phase anomalies in specific heat and thermal expansion. Below T(N) approximately 0.8 K antiferromagnetic superstructure peaks have been detected. The propagation vector of the magnetic order appears to be determined by the topology of the Fermi surface of heavy quasiparticles as indicated by renormalized band-structure calculations. The observation of long-range incommensurate antiferromagnetic order as the nature of the A phase in CeCu2Si2 suggests that a spin-density-wave instability is the origin of the quantum critical point in CeCu2Si2.     

Ultraviolet photosensitive response in an antimony-doped optical fiber

A silica optical fiber doped with Sb is fabricated with a refractive-index profile that is comparable with standard single-mode fiber. In D(2)-loaded samples, we observe UV photosensitivity with an initial refractive-index-modulation growth rate six times higher than that of the equivalent Ge-doped standard fibers. Enhanced temperature stability of the Bragg grating strength up to 200 degrees C is also observed. Grating growth kinetics in the Sb-doped fiber is compared with those of other Ge-doped photosensitive fibers.