Narrow Results

Three-dimensional fluorescence spectroscopy is a fast, nondestructive analysis method with good selectivity and high precision, which provides a foundation for the development of the current smart agriculture system. In modern agriculture, where agricultural information is fully perceived, it is still very difficult to quickly and destructively detect the internal chemical composition of soil, crops and agricultural products. Accurate determination of oil pollutants in water by using three-dimensional fluorescence spectroscopy technology can provide a basis for crop irrigation and is of great significance for improving agricultural benefits. The fluorescence spectrum analysis method is adopted to distinguish three kinds of mineral oil-gasoline, kerosene and diesel. In order to make the distinguishment more intuitive and convenient, a new identification method for mineral oil is proposed. The three-dimensional fluorescence spectra of the experimental dimension are reduced into two-dimensional fluorescence spectra. The concrete operations are as follows: adopting the method of end-to-end data matrix to constitute a large Ex image, and then figuring out the envelope curve, processing and analyzing the envelope image. Four factors, such as the ranges of excitation wavelength when the relative fluorescence intensity is greater than 0.5, the optimal excitation wavelengths, their kurtosis coefficients and skewness coefficients, are to be selected as the distinguishing feature parameters of mineral oil, and thus different kinds of mineral oil can be distinguished directly according to the feature parameters. The experimental results show that the proposed method has a high resolution for different kinds of mineral oil. Accurate and fast spectral data analysis methods can make up for the deficiencies of other agricultural information perception methods, provide a basis for the application of smart agriculture in many aspects and have a positive significance for promoting the comprehensive intelligent development of agriculture.

Given a family of objects in the plane, the line transversal problem is to compute a line that intersects every member of the family. In this paper we examine a variation of the line transversal problem that involves computing a shortest line segment that intersects every member of the family. In particular, we give O(n log n) time algorithms for computing a shortest transversal of a family of n lines, a family of n line segments, and a family of convex polygons with a total of n vertices. In general, finding a line transversal for a family of n objects takes Ω(n log n) time. This time bound holds for a family of n line segments as well as for a family of convex polygons with a total of n vertices. Hence, our shortest transversal algorithms for these families are optimal.

In this paper, we analyze the shapes of forward curves and yield curves that can be attained in the two-factor Vasicek model. We show how to partition the state space of the model, such that each partition is associated to a particular shape (normal, inverse, humped, etc.). The partitions and the corresponding shapes are determined by the winding number of a single curve with possible singularities and self-intersections, which can be constructed as the envelope of a family of lines. Building on these results, we classify possible transitions between term structure shapes, give results on attainability of shapes conditional on the level of the short rate, and propose a simple method to determine the relative frequency of different shapes of the forward curve and the yield curve.

A complex C of R-modules is called #-injective if all terms Cⁱ are injective R-modules for i ∈ ℤ. In this paper, we first give some characterizations and properties of #-injective complexes. Some relations between #-injective (pre)envelopes of a complex X and injective (pre)envelopes of the R-modules Xⁱ are also given. Finally, we study the -dimensions of complexes, where is the class of #-injective complexes.

A complex C is called Gorenstein cotorsion if Ext¹(G, C) = 0 for any Gorenstein flat complex G. It is shown that a complex C of left R-modules is Gorenstein cotorsion if and only if Cⁿ is Gorenstein cotorsion in R-Mod for all n ∈ ℤ and is exact for any Gorenstein flat complex G; and is a hereditary cotorsion theory over a right coherent ring R, where and denote the classes of all Gorenstein flat and Gorenstein cotorsion complexes respectively. Also Gorenstein cotorsion envelopes and Gorenstein flat covers of complexes are considered.

Given an $R$-module $C$ and a class of $R$-modules ${𝒟}$ over a commutative ring $R$, we investigate the relationship between the existence of ${𝒟}$-envelopes (respectively, ${𝒟}$-covers) and the existence of $\mathrm{\text{Hom}}(C,{𝒟})$-envelopes or $C\otimes {𝒟}$-envelopes (respectively, $\mathrm{\text{Hom}}(C,{𝒟})$-covers or $C\otimes {𝒟}$-covers) of modules. As a consequence, we characterize coherent rings, Noetherian rings, perfect rings and Artinian rings in terms of envelopes and covers by $C$-projective, $C$-flat, $C$-injective and $C$-$FP$-injective modules, where $C$ is a semidualizing $R$-module.

We prove several properties of kernels and cokernels in the category of augmented involutive stereotype algebras: (1) this category has kernels and cokernels, (2) the cokernel is preserved under the passage to the group stereotype algebras, and (3) the notion of cokernel allows to prove that the continuous envelope $\mathrm{\text{Env}}{{𝒞}}^{\star }(Z\cdot K)$ of the group algebra of a compact buildup of an abelian locally compact group is an involutive Hopf algebra in the category of stereotype spaces $(\mathrm{\text{Ste}},\odot )$. The last result plays an important role in the generalization of the Pontryagin duality for arbitrary Moore groups.

In this paper, by taking the class of all $C3$ (or $D3$) right $R$-modules for general envelopes and covers, we characterize a semisimple artinian ring (or a right perfect ring) via $D3$-covers (or $D3$-envelopes) and a right $V$-ring (or a right noetherian $V$-ring) via $C3$-covers (or $C3$-envelopes). By using isosimple-projective preenvelope, we obtained that if $R$ is a semiperfect right FGF ring (or left coherent ring), then every isosimple right $R$-module has a projective cover. Moreover, we also characterize semihereditary serial rings (respectively, hereditary artinian serial rings) in terms of epic flat (respectively, projective) envelopes.

We present a new criterion based on instantaneous frequency (IF) to distinguish mono-components (MCs). We first notice that the "offset of local extremum" caused by low-frequency envelope is often significant on envelope extraction, which determines the calculation of IF for MCs. We estimate the upper and lower bounds of the offset for a general family of signals. Conducted by the offset estimation, we propose a direct and effective algorithm to calculate IF. Our algorithm, which is based on an empirical pursuit of knots and natural splines, provides an accurate estimation of the envelope and derives a well-behaved IF. A theoretical explanation for the good approximation of proposed envelope is also stated. Experiment results show the fast convergence of our algorithm, which leads to a reliable IF and local mean to provide a flexible criterion for MC classification. We emphasize that it is important to pursue a certain balance among different requirements to define MC depending on specific applications.

In this paper, we consider two kinds of developable surfaces along a timelike frontal curve lying in a timelike surface in Minkowski 3-space, the Lorentz–Darboux rectifying surfaces and the Lorentz–Darboux osculating surfaces. Meanwhile, we also consider two curves generated by such a timelike frontal curve. We give two new invariants of the frontal curve which characterize singularities of the Lorentz–Darboux developable surfaces and Lorentz–Darboux rectifying and osculating curves. Unlike the regular curves, the frontal curves may have singular points. Using the methods of the unfolding theory in singularity theory, we complete the classifications of the singular points of these two surfaces and two curves. The main results indicate that compared with developable surfaces along a regular curve, there exists a more complicated construction for the singularities of the developable surfaces along a timelike frontal curve, there will appear an extra locus, arising by the singular point of the timelike frontal curve, for the singularities of the Lorentz–Darboux rectifying surface, whereas the Lorentz–Darboux osculating surface did not. In addition, we investigate the geometric properties of the timelike frontal curve, it is shown that the timelike frontal curve can be regarded as the envelope of a family of timelike frontal rectifying curves. Finally, we provide several examples to illustrate the theoretical results.

In this paper we study the existence of ℱℐ_n-envelopes, -envelopes and ℱℐ_n-covers, where ℱℐ_n denotes the class of all n-absolute pure modules for an integer n > 0 or n=∞. We prove that -envelopes and ℱℐ_n-covers exist over an n-coherent ring R, and ℱℐ₁-covers and special ℱℐ_n-preenvelopes exist over any ring R.

Reticuloendotheliosis virus (REV) infects various animals including chickens, ducks, geese, pheasants, peafowl and other birds. REV causes tumor, runting disease syndrome and immunosuppression in infected birds. The purpose of this study was to develop a rapid, reliable and convenient method to detect anti-REV antibody. The REV envelope protein was expressed by baculovirus expression system and evaluated for the potential as an antigen in an enzyme linked-immunosorbent assay (ELISA). The env gene from a REV strain goose/3410/06 was cloned into bacmid vector and expressed in Sf9 insect cells. The expected recombinant envelope protein expressed in infected insect cells was demonstrated in western blot with size of 62 kDa, and purified for using as antigen in an ELISA. A total of 182 chicken serum samples were used to evaluate the suitability of the ELISA based on neutralization test as the gold standard. The results showed that the relative sensitivity and relative specificity of this ELISA were 88.5% and 97.7%, respectively. The present ELISA using baculovirus expression envelope protein can be used to detect anti-REV antibody in the field.

It has been claimed that any expression of a(t) cosθ(t) with a(t) as the instantaneous amplitude and cosθ(t) as the carrier varying along with the phase θ(t) could not be uniquely defined. However, based on the fact that a(t) cosθ(t) with all its variational forms have the same numerical value at any given time, we propose the existence of a unique true intrinsic amplitude function a_i(t) and phase function θ_i(t) that a_i(t) cosθ_i(t) satisfying the envelope–carrier relationship is the only expression making physical sense. A constructive method is also presented to find such amplitude-phase pair uniquely from any Intrinsic Mode Function (IMF). As a result, we can treat any IMF in the form of a_i(t) cosθ_i(t) as the unique defined amplitude-phase pair, from which the instantaneous frequency (IF) can also be determined.

Empirical mode decomposition (EMD) lacks theoretical support. We propose a piecewise monotonous model for EMD, and prove that the trend-subtracting iteration converges and IMF-separating procedure ends up in finite steps under mild conditions. Experiments are implemented and compared with the classical EMD.

Classical Bézier curves (the parabolic case) with the natural barycentric description are considered. The explicit expressions for lenght, curvature, shape etc. are given. It is introduced the notion trajectory of Bézier curve and by means of the projective isotomic conjugation the corresponding envelope conic surfaces in the space are obtained.