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Stress response variability can cause up to 3-fold increase in the thermal resistance of Salmonella strains
Get PDFThe variability in the bacterial stress response has received plenty of attention during the last years, partly due to its relevance to microbial risk assessment. Although the microbial response is affected by numerous variability
sources, previous studies focused mostly on strain variability (inherent differences between strains of the same bacterial species) under optimal growth conditions. Here, we analyze a variability source relatively unexplored
within microbial risk assessment: stress response variability. This refers to physiological differences due to prior exposure to stressful environments. Namely, we studied the impact of sub-optimal pre-culture conditions or the application of an acid shock on the thermal resistance of two strains of Salmonella (a reference strain and a highly
heat resistant one). We observed that stress response variability is strain dependent. The heat resistance of the
reference strain had a significant increase in heat resistance (up to 3-fold increase), whereas the conditions tested resulted in a reduction of thermal resistance with respect to control conditions (up to 2-fold reduction). Considering that magnitude of these changes are comparable to strain variability, and that stress response
variability might be common throughout the food supply chain, this study evidences the need to study this
phenomenon further in order to incorporate it into quantitative microbial risk assessment
Stock market returns and crude oil price volatility: a comparative study between oil-exporting and oil-importing countries
Get PDFThis study employs a modern GARCH framework to conduct a comparative analysis of the volatility transmission between crude oil prices and a comprehensive set of financial assets, including sectoral equities, precious metals, and cryptocurrencies, across oil-exporting and oil-importing countries. Our central finding reveals a stark pre-pandemic dichotomy: before COVID-19, oil price volatility exhibited a significant positive correlation with nearly all sectoral stock returns in oil-exporting countries (the United States and Canada), reflecting a systemic, demand-driven linkage. In contrast, this relationship was largely insignificant in oil-importing countries (the United Kingdom, France, and Japan), with the exception of the energy sector. The COVID-19 crisis temporarily erased this fundamental distinction, as sectoral stock markets in both country groups moved in significant positive correlation with oil, driven by the synchronized global demand shock. This transition underscores that the oil–equity relationship is structurally determined by a country’s net oil trade position, a dynamic that can be overridden during systemic global crises. These findings offer crucial insights for international portfolio diversification and risk management
Experimental investigation of heat transfer coefficients in a plate heat exchange for an organic rankine cycle
Get PDFEnhancing the evaporator configuration of plate heat exchangers is essential for improving the overall efficiency of organic Rankine cycle (ORC) systems. To investigate the evaporator’s heat transfer characteristics, an experimental ORC test rig was developed. The experiments were conducted at saturation temperatures of 62.8–86.2 °C, mass fluxes of 5.0–16.6 kg/(m2·s), and heat fluxes of 3.1–9.2 kW/m2, spanning subcooled boiling, saturated two-phase, and superheating regions. The heat flux showed minimal variation with heat source temperature, whereas higher mass fluxes resulted in substantial increases in generator power and thermal efficiency due to enhanced convection and vaporization. The overall and refrigerant heat transfer coefficients rise with heat source temperature and mass flux, peaking under moderate conditions and declining as the superheating region becomes constrained. Comparison with existing correlations reveals pronounced deviations, indicating their limited applicability under the present operating conditions. A nondimensional correlation was established using dimensional analysis and multivariate regression to predict heat transfer across the subcooled boiling, saturated two-phase, and superheating regions. The proposed correlation yielded a mean absolute percentage error of 15.9%, demonstrating good predictive accuracy and providing a reliable theoretical basis for performance evaluation and design optimization of plate evaporators in ORC systems
Effect of forage characteristics on enteric methane emission across ruminant classes
No full textImproved forage quality is characterised by increased apparent total tract organic matter digestibility (ATTDOM) and CP content, and a decreased NDF content. Based on the meta-analysis conducted, we conclude that the effectiveness of reducing enteric CH4 emissions by improved forage quality differs across ruminant classes when CH4 is expressed relative to DMI, being effective in dairy cattle, but not in other cattle or small ruminants. When CH4 emission is expressed relative to DOMI, improved forage quality effectively reduces enteric CH4 emission across all ruminant classes, with ATTDOM and CP content negatively related and NDF content positively with CH4 yield (g/kg DOMI)
Skill and consistency of ECMWF forecasts of Atlantic tropical cyclone genesis
Get PDFWe evaluate the skill and jumpiness of the ECMWF medium-range ensemble (ENS) in predicting tropical cyclone genesis in the Atlantic basin. Focusing on the probabilistic performance of the ENS, we assess how far in advance the ENS can predict genesis, quantify the consistency (jumpiness) from run to run and investigate what factors influence the skill and consistency. We find that first indications of genesis are picked up at least 7 days ahead in 50% of the observed cases, although strong signals often only appear less than 3 days before genesis. There are significant regional differences, with observed genesis events predicted 2-3 days earlier in the eastern Atlantic than in other areas. The genesis probabilities can be jumpy from run to run and the jumpiest cases are in the more skilful regions (central and eastern Atlantic) and for situations where the initial signal for genesis appears at longer lead time. In the eastern Atlantic, there is a tendency for the ENS tracks to reach tropical storm strength earlier and further east than observed; this model bias can affect both skill and jumpiness of the genesis forecasts. Our results provide guidance to forecasters on how to use and interpret the ENS predictions. Areas for future work include the link between early intensification in the eastern Atlantic and African easterly wave activity, the relationship between skill and the TC development pathways, and the impact of systematic analysis differences between 0000 UTC and 1200 UTC on forecast intensity