微波辐射下无溶剂合成苯并咪唑-2-酮

以多聚磷酸(PPA)为催化剂,邻苯二胺和脲为原料,在微波辐射下无溶剂合成了苯并咪唑-2-酮,反应时间由2～3 h缩短到6～10 min,产率为62．81％;正交实验所得影响因素顺序为:微波功率>照射时间>原料配比>催化剂用量。最优化合成工艺条件为:n(邻苯二胺):n(脲)为1:2;微波功率为126 W;反应时间为7 min;数字熔点仪、红外光谱(IR)与核磁共振谱(1H NMR)等测试结果表明产物为苯并咪唑-2-酮。     

Sensory analysis to assess the freshness of Mediterranean anchovies (Engraulis encrasicholus) stored in ice

A quality index method and a sensory scheme were developed to assess raw and cooked Mediterranean anchovies (Engraulis encrasicholus), respectively. Fresh anchovies were stored in ice for 7 days in three trials. The changes in sensory punctuations showed satisfactory correlations with time of storage. Enterobacteria were the first microorganisms that exceeded the maximum allowable limit for marketable fish according to the Spanish regulations, reaching more than 10³ colony former units/g after 5 days of storage. Receiver operating characteristic curves of the sensory scores of raw and cooked anchovy against Enterobacteria counts were used to corroborate the suitability of the schemes. Areas under the curves were satisfactory and the estimated rejection values ranged from 0.43 to 0.51 and from 6.6 to 7.1 for raw and cooked anchovies, respectively.     

Theoretical and experimental investigation of flow and heat transfer in an internally-heated naturally-ventilated space

This paper presents the findings of a theoretical and experimental investigation of the thermodynamics of an internally heated control volume, ventilated by natural convection. A simple bench-type experiment has been used to determine the temperature history of the air, in support of a global calculation by numerical methods. Good agreement has been achieved between the experimental results and the mathematical prediction, which has wide ranging applications in practical situations.     

An experimental study on convection heat transfer from an array of discrete heat sources

Convection heat transfer from an array of discrete heat sources inside a rectangular channel has been investigated experimentally for air. The lower surface of the channel was equipped with 8×4 flush-mounted heat sources subjected to uniform heat flux; the sidewalls and the upper wall were insulated and adiabatic. The experimental parametric study was made for an aspect ratio of AR=2, Reynolds numbers 864≤Re_Dh≤7955, and modified Grashof numbers Gr*=1.72×10⁸ to 2.76×10⁹. From the experimental measurements, surface temperature distributions of the discrete heat sources were obtained and effects of Reynolds and Grashof numbers on these temperatures were investigated. Furthermore, Nusselt number distributions were calculated for different Reynolds and Grashof numbers. Results show that surface temperatures increase with increasing Grashof number and decrease with increasing Reynolds number. However, with the increase in the buoyancy affected secondary flow and the onset of instability, temperatures level off and even drop as a result of heat transfer enhancement. This outcome can also be observed from the variation of the row-averaged Nusselt number showing an increase towards the exit.     

Selectors Make Set-Based Analysis Too Hard

A set-based program analysis establishes constraints between sets of abstract values for all expressions in a program. Solving the system of constraints produces a conservative approximation to the program's runtime flow of values. Some practical set-based analyses use explicit selectors to extract the relevant values from an approximation set. For example, if the analysis needs to determine the possible return values of a procedure, it uses the appropriate selector to extract the relevant component from the abstract representation of the procedure. In this paper, we show that this selector-based approach complicates the constraint solving phase of the analysis too much and thus fails to scale up to realistic programming languages. We demonstrate this claim with a full-fledged value flow analysis for case-lambda, a multi-branched version of lambda. We show how both the theoretical underpinnings and the practical implementation become too complex. In response, we present a variant of set-based closure analysis that computes equivalent results in a much more efficient manner.     

Multiplicity of steady states in FCC units: effect of operating conditions

The FCC dynamics has been studied to determine the effect of operating conditions on multiplicity of steady states. The proposed model is capable to analyze several dynamic features to characterize the FCC process. Three combustion modes are analyzed: Partial combustion, total combustion and transition mode. At least three steady states have been determined in both partial and complete combustion modes. Furthermore, it is established in this paper that operating conditions are incapable to change the number of steady states. It is believed that a similar analysis should be applied to identify the effect on the multiplicity of physical parameters such as oxidation rates.     

Vibrational Mode in Two-Dimensional Dust Monolayer with Finite Size Dust Grains

Vibrational mode in a two-dimensional dust monolayer is investigated by considering the finite size of dust grains. Each dust grain is assumed to be a negative point charge and a dipole moment due to the inhomogeneous charge distribution on its surface. The dispersion relation of the vibrational mode is derived. Both the self-excited and externally excited cases are discussed. It is shown that the mode is sensitive to the direction of the dipole moment.     

WO3/CeO2/YSZ nanocomposite as a potential catalyst for methanol reforming

A WO₃/CeO₂/YSZ nanocomposite material [W/Zr nominal atomic ratio = 0.025, Ce/Zr nominal atomic ratio = 0.020] was prepared by wet impregnation and characterized by means of X-ray photoelectron and diffuse reflectance infrared Fourier transform spectroscopic techniques, X-ray diffraction and thermal analysis.Both tungsten and cerium oxides are significantly reduced at the interface with YSZ: Ce(III), in particular, seems to be the prevailing species.The interaction of the WO₃/CeO₂/YSZ nanopowder with pyridine and CO₂ allowed to investigate the acidic/basic sites. Weak contributions at 1602, 1625 and 1647 cm⁻¹ suggest the presence of Lewis and Brønsted acidic sites, whereas basic sites are not evidenced by the interaction with carbon dioxide. The presence of tungsten oxide causes the decrement of the acidic/basic sites, as indicated by the comparison with the results obtained on the CeO₂/YSZ support. Consistently, the interaction with methanol is mainly molecular.The oxidation of methanol was investigated both in the absence and in the presence of water. In the last case carbon dioxide starts forming from room temperature.     

Estimating standard errors of accuracy assessment statistics under cluster sampling

Cluster sampling is a viable sampling design for collecting reference data for the purpose of conducting an accuracy assessment of land-cover classifications obtained from remotely sensed data. The formulas for estimating various accuracy parameters such as the overall proportion of pixels correctly classified, the kappa coefficient of agreement, and user's and producer's accuracy are the same under cluster sampling and simple random sampling, but the formulas for estimating standard errors differ between the two designs. If standard error formulas appropriate for cluster sampling are not employed in an accuracy assessment based on this design, the reported variability of map accuracy statistics is likely to be grossly misleading. The proper standard error formulas for common map accuracy statistics are derived for one-stage cluster sampling. The validity of these standard error formulas is verified by a small simulation study, and the standard errors computed according to the usual simple random sampling formulas are shown to underestimate the true cluster sampling standard errors by 20–70% if the intracluster correlation is moderate.     

Brief Overview of Recent Developments on Negative Phase–Velocity Mediums (alias Left–Handed Materials)

This brief overview covers a rapidly occurring development in the area of microwave composite materials: isotropic dielectric–magnetic mediums wherein the phase velocity vector and the time–averaged Poynting vector are oppositely directed. Such materials have also been inappropriately designated as left–handed materials. Ramifications for aberration–free lenses, homogenization approaches, and complex mediums are also presented.