Effect of high and low glycaemic index recovery diets on intramuscular lipid oxidation during aerobic exercise

Intramyocellular lipid (IMCL) and plasma NEFA are important skeletal muscle fuel sources. By raising blood insulin concentrations, carbohydrate ingestion inhibits lypolysis and reduces circulating NEFA. We hypothesised that differences in the postprandial glycaemic and insulin response to carbohydrates (i.e. glycaemic index; GI) could alter NEFA availability and IMCL use during subsequent exercise. Endurance-trained individuals (n 7) cycled for 90 min at 70 % V?O2peak and then consumed either high GI (HGI) or low GI (LGI) meals over the following 12 h. The following day after an overnight fast, the 90 min cycle was repeated. IMCL content of the vastus lateralis was quantified using magnetic resonance spectroscopy before and after exercise. Blood samples were collected at 15 min intervals throughout exercise and analysed for NEFA, glycerol, glucose, insulin, and lactate. Substrate oxidation was calculated from expired air samples. The 90 min cycle resulted in >2-fold greater reduction in IMCL in the HGI trial (3·5 (sem 1·0) mm/kg wet weight) than the LGI trial (1·6 (sem 0·3) mm/kg wet weight, P < 0·05). During exercise, NEFA availability was reduced in the HGI trial compared to the LGI trial (area under curve 2·36 (sem 0·14) mEq/l per h v. 3·14 (sem 0·28) mEq/l per h, P < 0·05 respectively). No other differences were significant. The findings suggest that HGI carbohydrates reduce NEFA availability during exercise and increase reliance on IMCL as a substrate source during moderate intensity exercise

Four-wave mixing wavelength conversion efficiency in semiconductor traveling-wave amplifiers measured to 65 nm of wavelength shift

The efficiency of broadband optical wavelength conversion by four-wave mixing in semiconductor traveling-wave amplifiers is measured for wavelength shifts up to 65 nm using a tandem amplifier geometry. A quantity we call the relative conversion efficiency function, which determines the strength of the four-wave mixing nonlinearity, was extracted from the data. Using this quantity, gain requirements for lossless four-wave mixing wavelength conversion are calculated and discussed. Signal to background noise ratio is also measured and discussed in this study

Four-Wave Mixing in Semiconductor Traveling-wave Amplifiers for Efficient, Broadband, Wavelength Conversion up to 65 nm

Wavelength conversion is recognized as an important function in future fiber networks employing wavelength division multiplexing. The authors have recently demonstrated broad-band wavelength conversion over spans as large as 27 nm. Their approach uses ultra-fast four-wave mixing dynamics associated with intraband relaxation mechanisms in semiconductor traveling-wave amplifiers (TWA's). In the paper the authors present new results showing conversion over wavelength spans as large as 65 nm. This surpasses the previous record by over a factor of two. Of equal importance, they also verify experimentally their previous theoretical prediction that wavelength conversion efficiency varies as the cube of TWA single pass gain. In the course of our previous work, we have shown that the theoretical efficiency, η, of this process can be expressed by the simple relation: η = 3G + 2P + R(Δ⋋) where η is the ratio in dB of the converted signal output power to the signal input power and G is the single pass TWA optical gain. A crucial point is the presence of 3G in this expression - essentially, the wavelength converter uses the available TWA optimal gain three times. We verified this expression using an experimental setup similar to that described in. Tunable, single-frequency, erbium fiber ring lasers were used as pump and signal sources and TWA devices used contained tensile-strained mutli-quantum well active layers described in. Figure 1 shows conversion efficiency data plotted versus single-pass saturated optical gain. The pump power was -5.2 dBm and the signal power was -11.3 dBm. The measured slope of 3.18 confirms the cubic dependence of efficiency on single pass gain

Study of interwell carrier transport by terahertz four-wave mixing in an optical amplifier with tensile and compressively strained quantum wells

Interwell carrier transport in a semiconductor optical amplifier having a structure of alternating tensile and compressively strained quantum wells was studied by four-wave mixing at detuning frequencies up to 1 THz. A calculation of transbarrier transport efficiency is also presented to qualitatively explain the measured signal spectra

Efficiency of broadband four-wave mixing wavelength conversion using semiconductor traveling-wave amplifiers

We present a theoretical analysis and experimental measurements of broadband optical wavelength conversion by four-wave mixing in semiconductor traveling-wave amplifiers. In the theoretical analysis, we obtain an analytical expression for the conversion efficiency. In the experiments, both up and down-conversion efficiencies are measured as a function of wavelength shift for shifts up to 27 nm. The experimental data are well explained by the theoretical calculation. The observed higher conversion efficiency for wavelength down-conversion is believed to be caused by phase interferences that exist between various mechanisms contributing to the four-wave mixing process

Terahertz four-wave mixing spectroscopy for study of ultrafast dynamics in a semiconductor optical amplifier

Ultrafast dynamics in a 1.5-µm tensile-strained quantum-well optical amplifier has been studied by highly nondegenerate four-wave mixing at detuning frequencies up to 1.7 THz. Frequency response data indicate the presence of two ultrafast physical processes with characteristic relaxation lifetimes of 650 fs and <100 fs. The longer time constant is believed to be associated with the dynamic carrier heating effect. This is in agreement with previous time-domain pump-probe measurements using ultrashort optical pulses