Wang Dajun

Do Revised Giant Panda Population Estimates Aid in Their Conservation

Abstract The small number of giant pandas (Ailuropoda melanoleuca) in the world makes this the only species of bear classified as globally endangered on the IUCN red list. The latest rangewide population estimate was derived from scats (feces) found along transects throughout the geographic range of the species. Scats were differentiated into ∼1,600 individuals based on their geographical separation and the size of bamboo stem fragments contained within (reflective of bite-sizes). Recently, a team of researchers (Zhan et al. 2006) conducted genetic analysis of scats in a Chinese Nature Reserve (Wanglang). Their estimate of giant panda numbers there was double that obtained using the bite-size technique. Taking this to be representative of the entire range, they speculated that there could be 3,000 pandas in the wild. Many in the international conservation community heralded this as evidence that panda conservation is working well. Moreover, if the revised rangewide estimate is accepted as true, it could mandate the downlisting of pandas on the red list. We believe that such conclusions are unwarranted, or at least premature. First, the DNA-based estimate in the reserve may have been inflated by lack of geographic closure (which seems probable) and genotyping errors (which we found evidence of). Second, it was inappropriate to extrapolate results from this single point to the entire range of the species. The bite-size technique may substantially underestimate panda numbers in dense populations, such as in Wanglang Nature Reserve, where many nearby individuals likely have similar bite characteristics, whereas the technique may be more accurate in differentiating individuals in more sparsely populated areas. Although molecular-based population estimation is more rigorous than the bite-size method, too much uncertainty exists in the revised estimates to surmise either current population size or trend. We recommend (1) quantification of genotyping error rates for panda feces, (2) comparison of population estimates using bite-sizes and DNA derived from the same, short-term collection of scats, and (3) incorporation of both techniques in the next rangewide population estimate.

Crack detection of structure for plane problem with spatial wavelets

In this paper, the structure damage detection with spatial wavelets is approached. First, a plane stress problem, a rectangular plate containing a short crack under a distributed loading on the edge, is investigated. The displacement response data along the parallel and perpendicular lines at different positions from the crack are analyzed with the Haar wavelet. The peak in the spatial variations of the wavelets indicates the direction of the crack. In addition, a transverse crack in a cantilever beam is also investigated in the same ways. For these problems, the different crack positions are also simulated to testify the effectiveness of the technique. All the above numerical simulations are processed by the finite element analysis code, ABACUS. The results show that the spatial wavelet is a powerful tool for damage detection, and this new technique sees wide application fields with proad prospects.

Self-excited vibration of the shell-liquid coupled system induced by dry friction

The nonlinear vibration theory and the experimental modal analysis are used in this paper to study the self-excited vibration of the shell-liquid coupled system induced by dry friction. The effect of dry friction stick-slip coefficients and rubbing velocity on self-excited vibration, and the limit cycle and Hopf bifurcation solution of the system are obtained. In particular, it is shown that the phenomenon of 4 point (or 6 point) water droplet spurting of the Chinese cultural relic Dragon Washbasin is the result of the perfect combination of the self-excited vibration induced by dry friction and its special modes, which indicates the significant scientific value of the Chinese cultural relic Dragon Washbasin.

Approximate analytical solution of the self-excited vibration of piecewise-smooth systems induced by dry friction —The vibration mechanism of the Chinese cultural relic Dragon Washbasin

Based on our previous work, a mathematical model of piecewise-smooth systems is established by means of phase-plane orbit analysis, and it is then used to study the intersting phenomena of Chinese cultural relic Dragon Washbasin. The mechanism of nonlinear damping is analyzed; the approximate analytical solution of self-excited vibration of piecewise-smooth nonlinear systems induced by dry friction is derived by means of KB Method, the results of which agree well with that of the numerical solution. Therefore, the method presented in this paper is proved to be very efficient in analyzing the self-excited vibration of piecewise-smooth systems induced by dry friction.

The asymptotic properties of high frequencies for bars, beams and membranes

In this paper, a uniform analysis of the asymptotic properties of high frequencies of non-uniform bars, beams and circular membranes is given by using perturbation method, and the case of discontinuous physical parameters is also discussed.

Singularity under a concentrated force in elasticity

We first discuss singularity problem of a sort of partial differential equation involving δ function. Using this result we, then have the answer to various singularity problems in elasticity due to the presentation of a concentrated force. Lastly corresponding conclusions in vibration problem are drawn.

Active control of flexible beams subjected to multi-disturbance using one controller

The active control of vibration for a beam subjected to multi-disturbances is investigated based on wave propagating suppression. In this control system, there are the same numbers of the sensors, the signal inputting to the controller and the disturbances, but there is only one controller. It is a local control system, the system parameters depend only on the characteristics of the structure bounded by the sensors and the controller, and we need not take into account the boundary conditions and the properties of structures outside of this field. The system is efficient when a structure vibrates in middle and high frequency regions. Some control design rules are developed from the calculation results.

High-order self-excited vibration induced by dry friction between two elastic structures-Vibration mechanism of the Chinese culture relic dragon washbasin

Combining theoretical and experimental modal analyses on selfexcited vibration induced by dry friction between two elastic structures, we can explain the high-order sell-excited vibration phenomenon in which water droplets spurt from fourteen or twelve areas of the Chinese culture relic dragon washbasin when it is rubbed with hands, and clarify the mechanism of the singular high-order selfexcited vibration. The experimental modes and the practical measured results are presented for a special dragon washbasin. The theoretical results agree well with the experimental ones.