We obtain an approximate solution of Altarelli-Parisi equations yielding a sample of quantum chromodynamic structure function.
The SLAC-MIT data are analysed with it. Possible effects of intrinsic charm and higher twist are also included. Agreement
is found to be good forx⩾0.25. 相似文献
For any square-free positive integer m, let H(m) be the class-number of the field , where ζm is a primitive m-th root of unity. We show that if m = {3(8 g + 5)}2? 2 is a square-free integer, where g is a positive integer, then H(4 m) > 1. Similar result holds for a square-free integer m = {3(8 g +7)}2?2, where g is a positive integer. We also show that n|H(4 m) for certain positive integers m and n. 相似文献
We have been exploring the utilization of supported ceria and ceria–zirconia nano-oxides for different catalytic applications.
In this comprehensive investigation, a series of CexZr1−xO2/Al2O3, CexZr1−xO2/SiO2 and CexZr1−xO2/TiO2 composite oxide catalysts were synthesized and subjected to thermal treatments from 773 to 1073 K to examine the influence
of support on thermal stability, textural properties and catalytic activity of the ceria–zirconia solid solutions. The physicochemical
characterization studies were performed using X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy
(XPS), and high-resolution transmission electron microscopy (HREM), thermogravimetry and BET surface area methods. To evaluate
the catalytic properties, oxygen storage/release capacity (OSC) and CO oxidation activity measurements were carried out. The
XRD analyses revealed the formation of Ce0.75Zr0.25O2, Ce0.6Zr0.4O2, Ce0.16Zr0.84O2 and Ce0.5Zr0.5O2 phases depending on the nature of support and calcination temperature employed. Raman spectroscopy measurements in corroboration
with XRD results suggested enrichment of zirconium in the CexZr1−xO2 solid solutions with increasing calcination temperature thereby resulting in the formation of oxygen vacancies, lattice defects
and oxygen ion displacement from the ideal cubic lattice positions. The HREM results indicated a well-dispersed cubic CexZr1−xO2 phase of the size around 5 nm over all supports at 773 K and there was no appreciable increase in the size after treatment
at 1073 K. The XPS studies revealed the presence of cerium in both Ce4+ and Ce3+ oxidation states in different proportions depending on the nature of support and the treatment temperature applied. All characterization
techniques indicated absence of pure ZrO2 and crystalline inactive phases between Ce–Al, Ce–Si and Ce–Ti oxides. Among the three supports employed, silica was found
to stabilize more effectively the nanosized CexZr1−xO2 oxides by retarding the sintering phenomenon during high temperature treatments, followed by alumina and titania. Interestingly,
the alumina supported samples exhibited highest OSC and CO oxidation activity followed by titania and silica. Details of these
findings are consolidated in this review. 相似文献
The reaction of aldehyde with allylsilane in acetonitrile mediated by boron trifluoride etherate generated 4-aminotetrahydropyrans in good yields. The product is highly stereoselective. 相似文献
The reaction of Betti bases with various heterocycles in the presence of p-toluenesulphonic acid (PTSA) under microwave irradiation gives bis(heterocycle)methanes through benzyl transfer. The reaction proceeds via the cleavage of C-N bond followed by C-C bond. The metal-free cleavage of C-C bond, which is in fact a C-dearylation, is rarely reported in the literature. 相似文献
Let A??(n) denote the number of overpartitions of a non-negative integer n with no part divisible by ?, where ? is a positive integer. In this paper, we prove infinite family of congruences for A?5(n) modulo 4, A?6(n) modulo 3, and A?8(n) modulo 4. In the process, we also prove some other congruences. 相似文献
The reaction of [Rh(CO)2Cl]2 with 0.5 mol equivalent of the ligands [P′(X)(CH2-CH2P(X)Ph2)3](P′P3X4) {where X = O(a), S(b) and Se(c)} affords tetranuclear complexes of the type [Rh4(CO)8Cl4(P′P3X4)] (1a-1c). The complexes 1a-1c have been characterized by elemental analyses, mass spectrometry, IR and multinuclear NMR spectroscopy, and the ligands b and c are structurally determined by single crystal X-ray diffraction. 1a-1c undergo oxidative addition (OA) reactions with CH3I to generate Rh(III) oxidised products. Kinetic data for the reaction of 1a and 1b with excess CH3I indicate a pseudo first order reaction. The catalytic activity of 1a-1c for the carbonylation of methanol to acetic acid and its ester show a higher Turn Over Frequency (TOF = 1349-1748 h−1) compared to the well-known species [Rh(CO)2I2]− (TOF = 1000 h−1) under the similar experimental conditions. However, 1b and 1c exhibit lower TOF than 1a, which may be due to the desulfurization and deselinization of the ligands in the respective complexes under the reaction conditions. 相似文献
In the last few years, fluorescent nanodiamonds (FNDs) have been developed significantly as a new member in the nanocarbon family. The surface of FNDs is embedded with some crystallographic defects containing color centres which surmount the properties of other fluorochromes including up conversion and down conversion nanoparticles, quantum dots, nano tubes, fullerenes, organic dyes, silica etc. Some of the intriguing properties like inevitable photostability, inherent bio-compatibility, outstanding optical and robust mechanical properties, excellent magnetic field, and electric field sensing potentiality make FNDs appealing to some benevolent applications in numerous fields like bio-imaging, delivering drugs, fighting cancer, spin electronics, imaging of magnetic structure at nanoscale and as promising nanometric temperature sensor. The structure of FNDs has certain point defects on the surface among which negatively charged nitrogen vacancy centre (NV?) is the most investigated color centre. The production of NV? fluorescence nanodiamonds is the most challenging task as substitution of carbon atoms is required to create vacancies by causing irradiation from an electron beam which is followed by high temperature annealing. Thus, this review points out the relative advantages of FNDs containing negatively charged nitrogen vacancy centres produced from HPHT method or CVD method with those nanodiamonds produced through detonation process or pulsed laser ablation (PLA) method. The steps involved in the fabrication of FNDs are described along with the major challenges and struggles underwent during the process in this review. This review also summarizes the recent developments made in the functionalization and applications predominantly made in the field of biological science and it is understood that depending on the defect color centres they can exhibit different emitted wavelengths ranging from UV–visible to near infrared with broad or narrow bandwidths. This review also highlights some of the fluorescent NDs that emit stable and strong red or green photoluminescence from the defect centers of NV? which are implanted in the crystal lattice. This critical and extensive review will be useful for the further progress in this futuristic field of FNDs.
An efficient method for the synthesis of 2,3,5,6-tetrasubstituted tetrahydropyrans has been developed from the reaction of aldehydes and ethyl 2-(1-hydroxyalkyl/hydroxy(phenyl)methyl)-5-methylhex-4-enoate using (3,5)-oxonium-ene reaction promoted by boron trifluoride etherate in good yields under mild conditions. 相似文献
Bromoformyloxylation and bromoacetoxylation of olefins proceed smoothly and instantaneously in the presence of N,N-dibromo-p-toluene sulfonamide without any catalyst. The one step reactions can be carried out with all kinds of olefins in high yield and high regio and stereoselectivities. 相似文献