EXPERIMENTAL AND THEORETICAL RESEARCH OF ELECTRON EMISSION MECHANISM OF M-TYPE CATHODES

With the most advanced Synchronous Radiation Photoelectron Spectrum(SRPS),the emission mechanism of M-type cathodes has been investigated from the perspective of chemical state.Based on the experimental results of SRPS analysis,a new model of the electron emission mechanism for M-type cathode is discussed.The main topics in this paper include the research status of electron emission mechanism of M-type cathodes;the advantages of SRPS technology;the distribution of oxygen chemical state on the cathode surface and the evolvement of oxygen chemical state during activation process;the relation between barium chemical state and osmium(Os)-coating;surplus barium and its formula;the characteristics of Os,and other noble metal coatings;the relation between film characteristics and emission performance of cathodes,the inhibition effects to the emission for Platinum(Pt)-coated cathode,etc.At the end of this paper,electron emission mechanism of M-type cathode is summarized and foreseen.

Rapid quantification of acid value in frying oil using iron tetraphenylporphyrin fluorescent sensor coupled with density functional theory and multivariate analysis

A metalloporphyrin-based fluorescent sensor was developed to determine the acid value in frying oil.The electronic and structural performances of iron tetraphenylporphyrin(FeTPP)were theoretically investigated using time-dependent density functional theory and density functional theory at the B3LYP/LANL2DZ level.The quantified FeTPP-based fluorescent sensor results revealed its excellent performance in discriminating different analytes.In the present work,the acid value of palm olein was determined after every single frying cycle.A total of 10 frying cycles were conducted each day for 10 consecutive days.The FeTPP-based fluorescent sensor was used to quantify the acid value,and the results were compared with the chemical data obtained by conventional titration method.The synchronous fluorescence spectrum for each sample was recorded.Parallel factor analysis was used to decompose the three-dimensional spectrum data.Then,the support vector regression(SVR),partial least squares,and back-propagation artificial neural network methods were applied to build the regression models.After the comparison of the constructed models,the SVR models exhibited the highest correlation coefficients among all models,with 0.9748 and 0.9276 for the training and test sets,respectively.The findings suggested the potential of FeTPP-based fluorescent sensor in rapid monitoring of frying oil quality and perhaps also in other foods with higher oil contents.

Enzyme-free and multiplexed micro RNA detection using micro RNA-initiated DNA molecular motor

In this work,we have developed a sensitive,simple,and enzyme-free assay for detection of micro RNAs(mi RNAs)by means of a DNA molecular motor consisting of two stem-loop DNAs with identical stems and complementary loop domains.In the presence of mi RNA target,it can hybridize with one of the stem-loop DNA to open the stem and to produce a mi RNA/DNA hybrid and a single strand(ss)DNA,the ss DNA will in turn hybridize with another stem-loop DNA and finally form a double strand(ds)DNA to release the mi RNA.One of the stem-loop DNA is double-labeled by a fluorophore/quencher pair with efficiently quenched fluorescence.The formation of ds DNA can produced specific fluorescence signal for mi RNA detection.The released mi RNA will continuously initiate the next hybridization of the two stem-loop DNAs to form a cycle-running DNA molecular motor,which results in great fluorescence amplification.With the efficient signal amplification,as low as 1 pmol/L mi RNA target can be detected and a wide dynamic range from 1 pmol/L to 2 nmol/L is also obtained.Moreover,by designing different stem-loop DNAs specific to different mi RNA targets and labeling them with different fluorophores,multiplexed mi RNAs can be simultaneously detected in one-tube reaction with the synchronous fluorescence spectrum(SFS)technique.