Sequence and organization of the mitochondrial genome of an urostylidid bug,Urochela quadrinotata Reuter(Hemiptera:Urostylididae)

The complete mitochondrial genome of Urochela quadrinotata Reuter was sequenced and analyzed. This represents the first sequence completed for an insect in the family Urostylididae. The genome is 16585 bp in size and contains 35 genes （including 13 protein-coding genes, 20 transfer RNA genes, two ribosomal RNAs and a control region） with an A＋T content of 75.4%. Two tRNA genes, tRNATle and tRNAGln, are not detected in this genome. The gene order is similar to that most commonly found in insects. All tRNAs possess the typical clover-leaf structure, except tRNASer（AGN）, in which the dihydrouridine （DHU） arm forms a simple loop. The secondary structure of rrnL consists of six structural domains and 43 helices, and the rrnS includes three structural domains and 27 helices. An obvious feature of the control region is the presence of 1652 bp long tandem repeat sequences comprising 16 tandem repeat units.

Analysis of generation of cumulative second harmonics of Lamb modes in a layered planar structure

A technique for analyzing the nonlinear generation of the cumulative second har-monics of generalized Lamb modes in a layered planar structure is developed. A theoretical model for nonlinear generalized Lamb mode propagation in a layered planar structure has been established, based on a partial plane wave approach. The nonlinearity is treated as a second-order perturbation of the linear elastic response. This model reveals some interesting features of the physics of the cumulative second harmonic generation. Although Lamb mode propagation is dispersive in a layered structure, the results of this analysis show that the amplitudes of the second harmonics do accumulate with propagation distance under certain special conditions. On the basis of the boundary and initial conditions of excitation, the formal solution of the cumulative second harmonic has been derived. Using the formal solution, we have performed some numerical simulations and obtained the cumulative second harmonic field patterns, illus-trating the distortion effect along the propagation distance, as well as the dependence of the field patterns on the position of the excitation source.

A NUMERICAL METHOD FOR SECOND ORDER MEAN FORCES AND SLOWLY VARYING FORCES ON A FLOATING STRUCTURE

Existing far field expressions of second order potentials are by no means complete.Hence there has been no exact far field expression of second order potentials.In this paper the far field expression for Φ_d^((2)) is purposely avoided in deducing the formulae of second order forces and a series of functions Φ_(dRn)^((?)) are used.The far field expression of is given,which for (x,U,z)∈Σ,φ_(dRn)^((2))(?) φ_d^((2)).Using these properties formulae for calculating second order diffraction forces are obtained.To calculate the integral ∫∫_(?)1/g f_(?)Ψ_(?)ds it is divided into two parts.One is the integral over a finite domain and the function under the integral is continuous,so the usual approximate integration formulae may be used. The other is the integral over an infinite domain.Using the far field expression of first order potentials,formulae for calculating the integral to meet given accuracies are given. The mooring force in surge direction is used for comparison between numerical predictions and experimental measurements.The predicted results are checked against the measured value in a specially designed test.In the low frequency domain of interest,the mooring forces in surge,for calculated and experimental spectra are in good consistency so long as the damping coefficients is choosen appropriately.