Towards Omni-Tomography—Grand Fusion of Multiple Modalities for Simultaneous Interior Tomography

We recently elevated interior tomography from its origin in computed tomography (CT) to a general tomographic principle, and proved its validity for other tomographic modalities including SPECT, MRI, and others. Here we propose “omni-tomography”, a novel concept for the grand fusion of multiple tomographic modalities for simultaneous data acquisition in a region of interest (ROI). Omni-tomography can be instrumental when physiological processes under investigation are multi-dimensional, multi-scale, multi-temporal and multi-parametric. Both preclinical and clinical studies now depend on in vivo tomography, often requiring separate evaluations by different imaging modalities. Over the past decade, two approaches have been used for multimodality fusion: Software based image registration and hybrid scanners such as PET-CT, PET-MRI, and SPECT-CT among others. While there are intrinsic limitations with both approaches, the main obstacle to the seamless fusion of multiple imaging modalities has been the bulkiness of each individual imager and the conflict of their physical (especially spatial) requirements. To address this challenge, omni-tomography is now unveiled as an emerging direction for biomedical imaging and systems biomedicine

Far-field and beam characteristics of vertical-cavity surface-emitting lasers

We have determined the far-field patterns and beam parameters of vertical-cavity surface-emitting lasers (VCSELs) with different structures. The results show that the window diameter and the active-layer aperture of VCSELs strongly influence laser far-field distributions and beam characteristics; for VCSELs with small window omega=5 mu m, only one dominant lobe has been observed in the far-field profiles, even though injected current was increased up to 2 Ith; and the smaller the ratio of the window diameter to the active-layer aperture, the larger is the far-field divergence. The laser structure dependence of the K factor has also been studied. (C) 1996 American Institute of Physics

Invasive alien plants increase CH₄ emissions from a subtropical tidal estuarine wetland

Methane (CH4) is an important greenhouse gas whose emission from the largest source, wetlands is controlled by a number of environmental variables amongst which temperature, water-table, the availability of substrates and the CH4 transport properties of plants are most prominent and well characterised. Coastal wetland ecosystems are vulnerable to invasion by alien plant species which can make a significant local contribution to altering their species composition. However the effect of these changes in species composition on CH4 flux is rarely examined and so is poorly understood. Spartina alterniflora, a perennial grass native to North America, has spread rapidly along the south-east coast of China since its introduction in 1979. From 2002, this rapid invasion has extended to the tidal marshes of the Min River estuary, an area that, prior to invasion was dominated by the native plant Cyperus malaccensis. Here, we compare CH4 flux from the exotic invasive plant S. alterniflora with measurements from the aggressive native species Phragmites australis and the native species C. malaccensis following 3-years of monitoring. CH4 emissions were measured over entire tidal cycles. Soil CH4 production potentials were estimated for stands of each of above plants both in situ and in laboratory incubations. Mean annual CH4 fluxes from S. alterniflora, P. australis and C. malaccensis dominated stands over the three years were 95.7 (±18.7), 38.9 (±3.26) and 10.9 (±5.26) g m-2year-1, respectively. Our results demonstrate that recent invasion of the exotic species S. alterniflora and the increasing presence of the native plant P. australis has significantly increased CH4 emission from marshes that were previously dominated by the native species C. malaccensis. We also conclude that higher above ground biomass, higher CH4 production and more effective plant CH4 transport of S. alterniflora collectively contribute to its higher CH4 emission in the Min River estuary