Elevated CO₂ does not increase eucalypt forest productivity on a low-phosphorus soil

Rising atmospheric CO2 stimulates photosynthesis and productivity of forests, offsetting CO2 emissions. Elevated CO2 experiments in temperate planted forests yielded ~23% increases in productivity over the initial years. Whether similar CO2 stimulation occurs in mature evergreen broadleaved forests on low-phosphorus (P) soils is unknown, largely due to lack of experimental evidence. This knowledge gap creates major uncertainties in future climate projections as a large part of the tropics is P-limited. Here,we increased atmospheric CO2 concentration in a mature broadleaved evergreen eucalypt forest for three years, in the first large-scale experiment on a P-limited site. We show that tree growth and other aboveground productivity components did not significantly increase in response to elevated CO2 in three years, despite a sustained 19% increase in leaf photosynthesis. Moreover, tree growth in ambient CO2 was strongly P-limited and increased by ~35% with added phosphorus. The findings suggest that P availability may potentially constrain CO2-enhanced productivity in P-limited forests; hence, future atmospheric CO2 trajectories may be higher than predicted by some models. As a result, coupled climate-carbon models should incorporate both nitrogen and phosphorus limitations to vegetation productivity in estimating future carbon sinks

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

An asymmetrical connection balance transformer-based hybrid railway power conditioning system with cost-function optimization

For solving the emerging power quality problems in electrified railway, an asymmetrical connection balance transformer-based hybrid railway power conditioning system with cost-function optimization (ACBT-HRPC) is proposed in this paper. Compared with other balanced traction transformers, the ACBT is characterized with a much higher material utilization, which really matters in practical applications. Besides, the inductively filtered rectifier transformer, with filter-tuned branches used for filtering harmonics and compensating reactive power, is used as a coupling stage of hybrid railway power conditioning system. The mathematical relationship between power factor and design capacity is analyzed, and the cost-function optimization has been proposed to minimize the investment of ACBT-HRPC, which enables a satisfactory compensation performance with relatively attractive costs. Both the simulation and experimental results verify the effectiveness of ACBT-HRPC

A balance transformer integrated RPFC for ERPS power quality improvement with low design capacity

This paper gives the fundamental aspects of a power distribution scheme on railway power flow controller (RPFC) for the grid connection compatibility improvement in planning stage railway power system (RPS) via neatly adjusting the value and rotation direction of the primary three-phase current phasors for every given power factor and random load point. This method not only leads RPS to satisfy the relevant grid connection standards, but also can make RPFC have minimum designing capacity and high operating efficiency to decrease its costs in system planning stage. The analytic design method and the experimental results validate the correctness of the conception. The method of using this idea in more challenging serviced RPS will be discussed in another companion volume

Degradation of the Internal Elastic Laminae in Vein Grafts of Rats with Aortocaval Fistulae : Potential Impact on Graft Vasculopathy

The internal elastic lamina (IEL) of vein grafts may be modified when exposed to arterialized hemodynamics. We investigated changes of the IEL in the inferior vena cava (IVC) of rats with aortocaval fistulae (ACF). In the IVC of ACF rats, both a markedly increased flow velocity and a mildly increased pressure were demonstrated. In the lower segment where hemodynamic changes were prominent, neointimal hyperplasia was prominently found. The IEL of the IVC in sham-operated rats, observed by confocal microscopy, was composed of parallel elastic fibers. In ACF rats, the IEL degenerated progressively after surgery. The elastic fibers were stretched and gradually became sparse, a change that was more prominent in the lower segment. Eight weeks after surgery, the IEL hardly existed in some areas of the lower segment. Electron microscopy revealed decreased densities and diameters of elastic fibers. Reverse transcriptase-polymerase chain reaction analysis revealed an up-regulation of potent elastases, cathepsins K and S, and matrix metalloproteinase-2 in the IVC of ACF rats. Results of immunohistochemical studies localized cathepsin expression predominantly to the luminal endothelium lining the IEL, suggesting involvement of elastinolysis in the degradation of the IEL. We demonstrated the degradation of the IEL in the vein graft of ACF rats, especially in the segment exposed to prominent hemodynamic changes. IEL degradation may contribute to the development of neointimal hyperplasia in vein grafts