[Prevalence of upper respiratory tract group A Streptococcus carriage in school-age children from Tulufan City and Buerjin County of Xinjiang Province].

OBJECTIVE: To study the prevalence rate of upper respiratory tract group A Streptococcus (GAS) carriage in school-age children from Xinjiang Province. METHODS: A total of 478 children at age of 9-12 years from Tulufan City and Buerjin County of Xinjiang Province were enrolled by random cluster sampling. Throat swab cultures were performed once each season for the determination of presence of GAS. RESULTS: In the 1 827 samples, 196 GAS strains were isolated, with a GAS carrier rate of 10.7%. The prevalence rate of GAS carrier in Tulufan City ranged from 3.7%-16.5% compared with 4.7%-21.4% in Buerjin County (P < 0.05). The prevalence rate of GAS carrier in winter is the highest, followed by in autumn, spring and summer in both regions. There were significant differences in the GAS carriage rate in autumn between the two regions. There were no significant differences in the GAS carriage rate between boys and girls. Of the 196 GAS strains, 133 from Han, 22 from Uygur and 41 from Hazakh children. There were significant differences in the prevalence rate of GAS carriage among children with different ethic groups. CONCLUSIONS: The prevalence rate of GAS carriage is high in school-age children from Tulufan and Buerjin of Xinjiang Province. The GAS carrier rate is associated with the season and ethic group. The children from Buerjin County present a higher GAS carrier rate than those from Tulufan City.

[Epidemiological survey of rheumatic heart disease in schoolchildren in Guangdong and Xinjiang].

OBJECTIVE: To investigate the prevalence of rheumatic heart disease (RHD) among schoolchildren in Guangdong Province and Xinjiang Uygur Autonomous Region. METHODS: Using a cluster sampling method, an epidemiological survey of RHD was conducted in 16 682 primary and high school students by auscultation in Guangdong Province and Xinjiang Uygur Autonomous Region from 2005 to 2006. Review of the clinical records, RHD survey in adults, and examination of the positivity rate of group A beta-hemolytic Streptococcus (GAS) by throat swab cultures in the students aged between 9 and 12 years in the sampled schools were also carried out. RESULTS: No RHD patient was found in the sampled population. In Xinjiang, the prevalence of RHD was 12.9/1000 among adults, higher than that (2.2/1000) in Guangdong Province. The GAS-positive rate in the schoolchildren in Xinjiang ranged from 9.8% to 12.6%, higher than that in Guangdong (2.3%-3.9%). CONCLUSION: The GAS-positive rate among children and incidence of RHD in adults are higher in Xinjiang than in Guangdong. The prevalence of RHD among the schoolchildren shows a reduction compared with that in 1994.

Modeling of finite-amplitude sound beams: second order fields generated by a parametric loudspeaker.

The nonlinear interaction of sound waves in air has been applied to sound reproduction for audio applications. A directional audible sound can be generated by amplitude-modulating the ultrasound carrier with an audio signal, then transmitting it from a parametric loudspeaker. This brings the need of a computationally efficient model to describe the propagation of finite-amplitude sound beams for the system design and optimization. A quasilinear analytical solution capable of fast numerical evaluation is presented for the second-order fields of the sum-, difference-frequency and second harmonic components. It is based on a virtual-complex-source approach, wherein the source field is treated as an aggregation of a set of complex virtual sources located in complex distance, then the corresponding fundamental sound field is reduced to the computation of sums of simple functions by exploiting the integrability of Gaussian functions. By this result, the five-dimensional integral expressions for the second-order sound fields are simplified to one-dimensional integrals. Furthermore, a substantial analytical reduction to sums of single integrals also is derived for an arbitrary source distribution when the basis functions are expressible as a sum of products of trigonometric functions. The validity of the proposed method is confirmed by a comparison of numerical results with experimental data previously published for the rectangular ultrasonic transducer.

A complex virtual source approach for calculating the diffraction beam field generated by a rectangular planar source.

In this paper, a complex virtual source approach for calculating the ultrasound field generated by a rectangular planar source is presented. Instead of using a real rectangular plane source, the equivalent sources that have complex amplitudes in complex space are used to compute the sound field distribution. The parabolic equation first is solved in the kappa-space domain by applying Fourier transform. The kappa-space domain source is then expressed as a set of Gaussian functions, and the related coefficients is determined by the optimization method. The analytic solution then is derived, and the effect of the parameters on the calculation accuracy is discussed. The comparison between the proposed fast numerical scheme and previous methods (Fresnel integral and Ocheltree's method) and are given in an example. The numerical results reveal that the computation time in obtaining accurate calculations is greatly reduced by using the proposed method.