A fiber-optic strain gauge system for use in structural monitoring and smart-structure applications is described. The strain gauge uses a fiber-optic Bragg grating sensor to measure strain and a passive, wavelength demodulation system to determine the wavelength of the narrow-band, backreflected spectrum from the grating sensor. The fiber-optic strain gauge system permits the measurement of both static and dynamic strains with a noise-limited resolution of 0.44 microstrain/√Hz, a measurement dynamic range of 27.8 dB, and a bandwidth of 250 Hz.

To study the transition from the Paleolithic to the Neolithic period and its duration, samples of charcoal, bone, flowstone and shells excavated from Bailiandong and Miaoyan caves, Guangxi Zhuang autonomous region, South China were dated using the Peking University AMS facility and liquid scintillation counter. The remains excavated from these sites show typical characteristics of the transition from the Paleolithic to the Neolithic. Radiocarbon dating results show a rapid transition from ca. 20 to 10 ka bp.

An optical-fiber Michelson interferometric acoustic emission sensor is described. The sensor uses ordinary singlemode fiber and is embedded in the composite material under test. Signals are demodulated through the active homodyne. This system provides a novel approach for material nondestructive evaluation.

Abstract. Arable soils may act as a sink in the global carbon cycle, but the prediction of their potential for carbon sequestration remains challenging. Amongst other factors, soil aeration is known to influence root growth and microbial activity and thus inputs and decomposition of soil organic carbon. However, the influence of soil aeration on soil organic carbon content has been explored only little, especially at the farm level. Here, we investigated relationships between gas transport properties and organic carbon content in the topsoil and subsoil of 30 fields of individual farms, covering a wide range of textural composition. The fields were managed either conventionally, organically, or according to no-till practice. Despite considerable overlap between the management systems, we found that tillage increased soil gas transport capability in the topsoil, while organic farming resulted in higher soil organic carbon content. Remarkably, higher gas transport capability was associated with higher soil organic carbon content, both in the topsoil and subsoil (0.53 < R2 < 0.71). Exogenous organic carbon inputs in the form of crop residues and organic amendments, in contrast, were not related to soil organic carbon content. Based on this, we conjecture that higher gas transport capability resulted in improved conditions for root growth, which eventually led to increased input of soil organic carbon. Our findings show the importance of soil aeration for carbon storage in soil and highlight the need to consider aeration in the evaluation of carbon sequestration strategies in cropping systems.