RESUMO
This paper is concerned with the propagation of Rayleigh waves in a compressible orthotropic half-space coated by a compressible orthotropic layer. The main purpose of the paper is to establish an explicit exact formula for the H/V ratio (the horizontal-to-vertical displacement ratio) of the Rayleigh wave. This formula is derived by using the transfer matrix for an orthotropic elastic layer and by the effective boundary condition technique. The formula recovers the H/V formula by Malischewsky and Scherbaum [(2004). Wave Motion 40, 57-67] for the compressible isotropic case and the H/V formula by Love [(1911). Some Problems of Geodynamics (Cambridge University Press, Cambridge)] for the incompressible isotropic case. The effect of anisotropy on the H/V ratio's properties is examined and it is numerically shown that the anisotropy strongly affects the peak and zero frequency of the H/V ratio and its prograde domain as well. As the H/V ratio is a dimensionless quantity and it is easily experimentally measured, the obtained formula will be a useful tool for the nondestructive evaluation of mechanical properties of thin films deposited onto half-spaces. Two numerical examples are performed to show how the obtained formula can be used to extract the material properties of deposited layers from measured values of the H/V ratio.
RESUMO
Antimicrobial use (AMU) and antimicrobial resistance (AMR) are a growing public health and economic threat in Vietnam. We conducted a pilot surveillance programme in five provinces of Vietnam, two in the south and three in the north, to identify antimicrobial resistance (AMR) in rectal swab samples from pigs and fecal samples from chickens at slaughter points during three different points in time from 2017 to 2019. Escherichia coli (E. coli) and non-typhoidal Salmonella (NTS) isolates were tested for antimicrobial susceptibility using disk diffusion assay for 19 antimicrobial agents belonging to nine antimicrobial classes and Etest for colistin (polymyxin). Almost all E. coli (99%; 1029/1042) and NTS (96%; 208/216) isolates were resistant to at least one antimicrobial agent; 94% (981/1042) of E. coli and 89% (193/216) of NTS isolates were multidrug-resistant (MDR). Higher proportions of E. coli and NTS isolated from chickens were resistant to all antimicrobial classes than those isolates from pigs. There was a significantly higher proportion of MDR NTS isolates from the southern provinces of Ho Chi Minh City and Long An (p = 0.008). Although there were increasing trends of NTS in proportion of resistance to fluoroquinolone over the three surveillance rounds, there was a significant decreasing trend of NTS in proportion of resistance to polymyxin (p = 0.002). It is important to establish an annual AMR surveillance program for livestock in Vietnam to assess the impact of interventions, observe trends and drive decision making that ultimately contributes to reducing AMR public health threat.
RESUMO
We investigated the effects of Mn doping on the crystal structure, phonon vibration, and magnetic properties of Bi0.88Sm0.12FeO3 ceramics. Mn doping effectively modified the rhombohedral symmetry and induced a structural transition from an R3c rhombohedral to Pnam orthorhombic structure. Magnetic measurements revealed a weak ferromagnetic behavior, which was related to the canted antiferromagnetic order of the Pnam structure. The cycloidal spin structure of the R3c phase could not be suppressed by substitution of Mn at the Fe site. Studies on the self-phase transition and electric field-induced structural transition revealed many changes in coercivity and remanent magnetization, which are believed to originate from the R3c/Pnam phase switching along with spin frustration. Observations of the field step-dependent hysteresis loop and the ferromagnetic-like hysteresis loop after poling in an electric field provided direct evidence of phase boundary (PB) ferromagnetism and magnetic coupling at the PB.