A novel and efficient synthesis of N-substituted pyrrolo-pyrazinone derivatives has been developed. A trichloroacetyl group connected to the pyrrole ring was converted into the desired carboxamide derivatives. Promoted by NaH, the pyrrole carboxamide derivatives underwent a tandem reaction with propargyl bromide to afford pyrrolo-pyrazinones with high efficiency under very mild conditions. The mechanism for the formation of the products is discussed and supported by DFT calculations. 相似文献
The two-dimensional organic conductor
κ-(BEDT-TTF)2Cu[N(CN)2]BrxCl1-x undergoes a
transition from an insulator to a superconductor upon substituting
Cl by Br. We have performed in- and out-of-plane
electric-transport measurements on the alloyed series with x =
20%, 40%, 70%, 80%, 85%, and 90% as a function of
temperature in order to explore the bandwidth-controlled phase
transition between the Mott insulator and the Fermi-liquid. All
crystals exhibit a similar semiconducting behavior of ρ(T)
from room temperature down to 100 K. Below approximately 50 K, a
metal-to-insulator transition is found for compounds with x < 70%. Out of this Mott insulating state, magnetic order develops
below TN≈ 25 K. The Br-rich samples cross a bad-metal
regime before they become coherent metals and eventually
superconducting at Tc≈ 12 K. For these systems the
resistivity at Tc≤T≤T0 reveals a ρ(T) ∝ T2 dependence associated with a strongly correlated
Fermi-liquid, limited by some characteristic temperature T0.
The conclusions are corroborated by data from microwave, magnetic
and optical experiments. 相似文献
A greedy algorithm in combination with radial basis functions partition of unity collocation (GRBF‐PUC) scheme is used as a locally meshless method for American option pricing. The radial basis function partition of unity method (RBF‐PUM) is a localization technique. Because of having interpolation matrices with large condition numbers, global approximants and some local ones suffer from instability. To overcome this, a greedy algorithm is added to RBF‐PUM. The greedy algorithm furnishes a subset of best nodes among the points X. Such nodes are then used as points of trial in a locally supported RBF approximant for each partition. Using of greedy selected points leads to decreasing the condition number of interpolation matrices and reducing the burdensome in pricing American options. 相似文献
Rare earth element substituted bismuth ferrites (BiFeO3) are of enormous importance as magnetoelectric materials. The polycrystalline samples of BixLa1−xFeO3 (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of
these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz
to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz).
All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature
shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds
to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity
as well as ε′ are found to be maximum for the sample x=0.2 at room temperature. 相似文献
CoFe2O4-BaTiO3 composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases
in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in
the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac
conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric
conversion factor has been studied as a function of magnetic field. 相似文献
We used the technique of the separation of Coulomb and diffraction dissociation of incident heavy ion to select the events due to induced neutron from 16O leaving sub-oxygen nucleus to break-up. The characteristics of these events of neutron emulsion collisions are displayed and compared with that obtained from incident proton at the same energy.
The studied interactions are classified according to the type of target nucleus (H, CNO and AgBr) by using the method of separation. Cascade-evaporation model (CEM) calculations are taken into account and compared with that obtained from the interactions of induced neutron from 16O (4.5 A GeV/c) with emulsion nuclei and with the results of incident proton at the same target and energy. CEM can describe the distributions of proton and neutron interactions. It is conjuctured that it may be possible to develop a similar theoretical model based on the modern methods of nonlinear dynamics, neural network and complexity [Randomness and Undecidability in Physics, World Scientific, Singapore, 1993]. 相似文献
Magnetically guided drug transportation is a technique in which magnetic pharmaceutical transporters in organisms are controlled by applied magnetic forces to deliver drugs to the desired location. Different magnetic drug delivery systems (MDDSs) are developed to treat a variety of illnesses, particularly cancer and neurological disorders. However, a unique magnetic setup is required in each application for an effective magnetically guided drug aiming to direct the drug-carrying nanocarriers to the intended area. The current and future perspectives of MDDS are investigated in this study by considering their biological functions, deliverable efficiency, complexity, and the nature of the externally applied magnetic field. Despite the fact that MDDSs have low cytotoxicity, regulated magneto reactivity, extended circulation lifespan, and high surface stability, very few clinical studies have been conducted to date in order to achieve optimized therapeutic efficacy before entering the market. In recent studies, the development of novel magnetic medication transporting carriers is preferred over direct magnetic medication administration. Better functional magnetic targeting technologies are required for such breakthroughs to enter clinical trials. Because MDDSs are unlikely to work in all clinical situations, more focused research is needed to replace or improve the strategy for treating multiple illnesses. 相似文献
In this study, the problem of steady state natural convection in an enclosure filled with a nanofluid has been analyzed numerically by using heating and cooling by sinusoidal temperature profiles on one side. The governing partial differential equations, in terms of the dimensionless stream function–vorticity and temperature, are solved numerically using the finite volume method for various inclination angles 0°≤?≤90°, different types of nanoparticles (TiO2 and Al2O3) and fractions of nanoparticles 0≤φ≤0.1, whereas the range of the Rayleigh number Ra is 103–105. It is found that the addition of nanoparticles into water affects the fluid flow and temperature distribution especially for higher Rayleigh numbers. An enhancement in heat transfer rate was registered for the whole range of Rayleigh numbers. However, low Rayleigh numbers show more enhancement compared to high Rayleigh numbers. 相似文献
Speciation studies are much more important than total element determination because toxicity of many elements depends on their chemical forms. Nobody can claim that a foodstuff is very dangerous to eat by determining total arsenic due to the possibility that the arsenic could be present in non-toxic forms. Hence, speciation studies are crucial in any matrix relevant to human beings.Trace-element speciation requires sufficiently sensitive procedures to monitor each species at trace levels. One way to increase the sensitivity for elements forming volatile species is coupling high-performance liquid chromatography (HPLC) with chemical-vapor generation (CVG). This review aims to highlight not only development of HPLC-CVG techniques for ultratrace-elemental speciation in a variety of matrices but also their application. In addition, we discuss the advantages and the disadvantages of these techniques. 相似文献