Accounting for temporal changes in carbon dioxide (CO 2 ) emissions from freshwaters remains a challenge for global and regional carbon budgets. Here, we synthesize 171 site-months of eddy covariance flux measurements of CO 2 from 13 lakes and reservoirs in the Northern Hemisphere (NH) and quantify the magnitude and dynamics at multiple temporal scales. We found pronounced diel and sub-monthly oscillatory variations in CO 2 flux at all sites. Diel variation converted sites to daily net sinks of CO 2 in only 11% of site-months. Upscaled annual emissions had an average of 25% (range 3-58%) interannual variation. Given temporal variation remains under-represented in inventories of CO 2 emissions from lakes and reservoirs, revisions in CO 2 flux are needed using a better representation of sub-daily to interannual variability. Constraining short-and long-term variability is necessary to improve detection of temporal changes of CO 2 fluxes in response to natural and anthropogenic drivers.

Purpose:To devise an efficient strategy for the separation and recovery of high-quality γ-PGA by investigation of the physical properties, pigment properties and microfiltration mode of high-viscosity fermentation broth. Methods: The bacterial strain, Bacillus subtilis 115, was used in this study. The viscosity of the fermentation broth was determined by digital viscometer with spindle SP-2 at 25 o C. The concentrations of glucose and L-glutamate were analyzed with a biosensor equipped with both glucose oxidase and Lglutamate oxidase electrodes. The pigment in the fermentation liquid was scanned with a UV spectrophotometer at wavelength range of 200 -500 nm and was removed using activated carbon. Measurement of IR spectrum was performed using an IR spectrophotometer with KBr pellet. . Results:The results showed that the γ-PGA yield was 35 g/L. The viscosity of the fermentation broth was 1600 mPa.s at the end of the batch fermentation. After 3-fold dilution, the viscosity was reduced to one-fortieth of the original value at 65 °C for 30 min., which allowed effective removal of Bacillus subtilis 115 from the broth. Maximum UV absorption of the pigment was occurred at 260 nm. The pigment was removed by shaking with 0.6 % activated carbon powder at 50 rpm for 20 min, resulting in 88 % decolorization. Concentration with hollow-fiber membrane (MWCO 500,000) resulted in complete removal of residual glucose and glutamic acid from the aqueous solution of γ-PGA. The molecular weight of the γ-PGA was 1095 kDa, and its UV scanning spectrum showed an absorption peak at 216 nm. The decomposition temperature (Td) of the γ-PGA was 312.92 oC. Its IR spectrum was consistent with the presence of carboxyl, hydroxyl, carbonyl and amide groups. Conclusion: An efficient method for the extraction and purification of high-quality γ-PGA from highviscosity fermentation broth.

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This paper addresses the adaptive asymptotic tracking control problem for nonlinear systems whose virtual control gains are unknown nonlinear functions of system states. Only in the first step, the Nussbaum gain technique is utilized to handle the uncertain virtual control gain. In the remaining steps, virtual control gains are dealt with by constructing novel control laws without the approximation of the uncertain nonlinear functions and external disturbances by neural networks or fuzzy logic. New adaptive laws are defined to compensate for unknown virtual control gains, uncertain parameters, and external disturbances. Finally, an adaptive tracking controller is designed and applied to the control of a 3-order robot system, which guarantees the boundedness of all the signals in the closed-loop system and asymptotic stability of the tracking error.