Aims/hypothesis We tested the hypothesis that the reversibility of insulin resistance and diabetes observed after biliopancreatic diversion (BPD) is related to changes in circadian rhythms of gastrointestinal hormones. Methods Ten morbidly obese participants, five with normal glucose tolerance (NGT) and five with type 2 diabetes, were studied before and within 2 weeks after BPD. Withinday variations in glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP1) levels were assessed using a single cosinor model. Insulin sensitivity was assessed by euglycaemic-hyperinsulinaemic clamp.Results Basal GLP1 relative amplitude (amplitude/ mesor× 100) was 25.82-4.06% in NGT; it increased to 41.38-4.32% after BPD but was unchanged in diabetic patients. GLP1 and GIP mesor were shifted in time after surgery in diabetic patients but not in NGT participants. After BPD, the GLP1 AUC significantly increased from 775± 94 to 846± 161 pmol l −1 min in NGT, whereas GIP AUC decreased significantly from 1,373± 565 to 513± 186 pmol l −1 min in diabetic patients. Two-way ANOVA showed a strong influence of BPD on both GIP (p =0.010) and GLP1 AUCs (p =0.033), which was potentiated by the presence of diabetes, particularly for GIP (BPD× diabetes, p =0.003). Insulin sensitivity was markedly improved (p< 0.01) in NGT (from 9.14± 3.63 to 36.04 ±8.55 µmol [kg fat-free mass] −1 min −1 ) and diabetic patients (from 9.49± 3.56 to 38.57± 4.62 µmol [kg fat-free mass] −1 min −1 ). Conclusions/interpretation An incretin circadian rhythm was shown for the first time in morbid obesity. The effect of BPD on the 24 h pattern of incretin differed between NGT and diabetic patients. GLP1 secretion impairment was reversed in NGT and could not be overcome by surgery in diabetes. On the other hand, GIP secretion was blunted after the operation only in diabetic patients, suggesting a role in insulin resistance and diabetes.Keywords Bariatric surgery . Circadian rhythm . GIP . GLP1 . Morbid obesity Abbreviations BPDBiliopancreatic diversion FFM Fat-free mass GIP Glucose-dependent insulinotropic polypeptide GLP1 Glucagon-like peptide 1 NGT Normal glucose tolerance RYGB Roux-en-Y gastric bypass Diabetologia (2009) 52:873-881

Energy storage has been identified as a priority technology for innovation. However, the rapidly developing family of storage technologies will find it difficult, under the current regulatory regimes, to compete with conventional generators for the provision of electricity system services, and this is likely to impede innovation. This paper analyses and categorizes 16 investment barriers hindering the near-term deployment of energy storage technologies in electricity markets, which are related to four regulatory and public attitudes barriers.The most important regulatory barrier is the current classification of storage as a generation asset, despite it being unable to provide a positive net flow of electricity, which is used to justify double network usage charges. The merit order design of balancing and ancillary markets makes it difficult for storage technologies to recoup their relatively high capital cost, while capacity markets penalize their limited discharge duration. Network companies are in the best position to realize the system value of storage, but their ownership may only be acceptable if system operation is made independent of network operation.Current initiatives to address these issues include flexible connection agreements and the development of enhanced frequency response and aggregate fast reserve services. However, to remove the identified barriers, a market structure that valued the flexibility offered by storage, viewing it as complementing rather than competing with network and generation assets, would be required.

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Energy storage can make key contributions to balancing future low-carbon energy systems by providing a variety of energy system services, with batteries expected to be widely deployed as costs fall with innovation. This paper assesses whether synergies exist between two of the most significant of these services, fast frequency response and energy arbitrage, if a battery energy storage system (BESS) is used to deliver both. A techno-economic model is developed to simulate 600 possible fast frequency response availability windows. Results show that two distinct synergies exist between the two services. The first synergy accounts for the possibility of charging outside the deadband for delivering fast frequency response. We propose an innovative state-of-charge management strategy to exploit this synergy. The second synergy results from energy arbitrage revenues being highly concentrated around peak times, which can enable a battery system to capture most of the arbitrage revenues without an excessive reduction in revenues from capacity provision with enhanced frequency response. The combination of these two synergies means that a battery system could increase its operating profits by 25% by delivering arbitrage and frequency response alternately. This result is shown to be statistically robust using historical data. A battery system able to discharge for 1.5-2 h at its full power rating will most most likely optimise these synergies.