Flashback, burning velocities and hydrogen admixture:Domestic appliance approval, gas regulation and appliance development

Introducing natural gas/hydrogen mixtures to an installed population of domestic natural gas appliances necessarily implies considering the risk of flashback. Previously, we quantified this risk via an interchangeability analysis using calculated laminar burning velocities. With an increasing contribution of renewable energy, still higher hydrogen fractions will become of interest to improve the economic viability in power-to-gas chains. To extend the possibilities for hydrogen admixture beyond the limits given by extant ranges of Wobbe Index and burning velocity, appliance approval standards and gas regulations must be examined to assess the degree to which higher hydrogen fractions are, or can be, justified. However, the current standards and regulations do not consider the risk of flashback in terms of the laminar burning velocity explicitly, leaving the justification of higher hydrogen fractions to empirical observations followed when the approval standards were codified. Here, we reframe the approval and regulation standards in terms of the calculated laminar burning velocity, which quantifies the notion of a 'safety margin' to safeguard appliance performance with respect to flashback, for a group of natural gases that is commonplace in the European Union (EU) but representative for many international situations. The method presented can be applied for any local regulatory area. In plots of burning velocity vs. equivalence ratio, ranges of regulated gas qualities are represented as a curve for natural gases, while for natural gas/hydrogen mixtures they appear as areas indicating the variations in hydrogen fraction for different gas compositions that do not increase the risk of flashback. To quantify the safety margin, the approval gas used in the EU for flashback (G222) is taken as an example, because of the many decades of experience in using this gas to safeguard appliance performance. Using the assumed range of gas quality and approval gas as an example, for appliances whose primary equivalence ratio is fuel rich (at greatest risk for flashback), a safety margin of 11.5 cm/s is determined and used in analyses for determining the composition of flashback limit gases in approval standards for a situation in which higher hydrogen fractions are desired. Situations considering both variable and constant fractions of hydrogen in natural gas are examined. The end-use demand for a minimum degree of thermal comfort, by having a minimum Wobbe Index in the regulated range of gas quality, automatically complicates grid management schemes for hydrogen addition: the maximum hydrogen admixture is necessarily coupled to the composition of the natural gas to which it is added. The only solution for having a constant hydrogen fraction without regard to the gas composition is by relaxing this demand on thermal comfort; in the example used here, 20% hydrogen admixture reduces the thermal comfort in the worst case by 4.7%. Fuel suppliers, grid operators and end users must agree to this loss of fitness for purpose to maximize the decarbonization of the gas supply by hydrogen admixture

Lifetime-Limited Photochemical Hole-Burning in s-Tetrazine-Benzene Mixed Crystals at 2 K

We show that the technique of photochemical hole-burning can be utilized to measure sub-nanosecond fluorescence lifetimes of molecular excited states. s-tetrazine is taken as an example and from the width of the hole (0.7 ± 0.1 GHz), burned in the origin of the lowest 1B3u ← 1A1g transition at 2 K in a benzene mixed crystal, a fluorescence lifetime of 455+75-55 ps is obtained. The coherence lifetime of the 16 a02 vibronic transition is found to be 25 ps

The role of ATM and 53BP1 as predictive markers in cervical cancer

Treatment of advanced-stage cervical cancers with (chemo)radiation causes cytotoxicity through induction of high levels of DNA damage. Tumour cells respond to DNA damage by activation of the DNA damage response (DDR), which induces DNA repair and may counteract chemoradiation efficacy. Here, we investigated DDR components as potential therapeutic targets and verified the predictive and prognostic value of DDR activation in patients with cervical cancer treated with (chemo)radiation. In a panel of cervical cancer cell lines, inactivation of ataxia telangiectasia mutated (ATM) or its substrate p53-binding protein-1 (53BP1) clearly gave rise to cell cycle defects in response to irradiation. Concordantly, clonogenic survival analysis revealed that ATM inhibition, but not 53BP1 depletion, strongly radiosensitised cervical cancer cells. In contrast, ATM inhibition did not radiosensitise non-transformed epithelial cells or non-transformed BJ fibroblasts. Interestingly, high levels of active ATM prior to irradiation were related with increased radioresistance. To test whether active ATM in tumours prior to treatment also resulted in resistance to therapy, immunohistochemistry was performed on tumour material of patients with advanced-stage cervical cancer (n = 375) treated with (chemo)radiation. High levels of phosphorylated (p-)ATM [p = 0.006, hazard ratio (HR) = 1.817] were related to poor locoregional disease-free survival. Furthermore, high levels of p-ATM predicted shorter disease-specific survival (p = 0.038, HR = 1.418). The presence of phosphorylated 53BP1 was associated with p-ATM (p = 0.001, odds ratio = 2.206) but was not related to any clinicopathological features or survival. In conclusion, both our in vitro and patient-related findings indicate a protective role for ATM in response to (chemo)radiation in cervical cancer and point at ATM inhibition as a possible means to improve the efficacy of (chemo)radiation

Does visual cortex lactate increase following photic stimulation in migraine without aura patients? A functional 1H-MRS study

Proton magnetic resonance spectroscopy (1H-MRS) has been used in a number of studies to assess noninvasively the temporal changes of lactate (Lac) in the activated human brain. Migraine neurobiology involves lack of cortical habituation to repetitive stimuli and a mitochondrial component has been put forward. Our group has recently demonstrated a reduction in the high-energy phosphates adenosine triphosphate (ATP) and phosphocreatine (PCr) in the occipital lobe of migraine without aura (MwoA) patients, at least in a subgroup, in a phosphorus MRS (31P-MRS) study. In previous studies, basal Lac levels or photic stimulation (PS)-induced Lac levels were found to be increased in patients with migraine with aura (MwA) and migraine patients with visual symptoms and paraesthesia, paresia and/or dysphasia, respectively. The aim of this study was to perform functional 1H-MRS at 3 T in 20 MwoA patients and 20 control subjects. Repetitive visual stimulation was applied using MR-compatible goggles with 8 Hz checkerboard stimulation during 12 min. We did not observe any significant differences in signal integrals, ratios and absolute metabolite concentrations, including Lac, between MwoA patients and controls before PS. Lac also did not increase significantly during and following PS, both for MwoA patients and controls. Subtle Lac changes, smaller than the sensitivity threshold (i.e. estimated at 0.1–0.2 μmol/g at 3 T), cannot be detected by MRS. Our study does, however, argue against a significant switch to non-aerobic glucose metabolism during long-lasting PS of the visual cortex in MwoA patients