Singlet exciton fission is a process that occurs in select organic semiconductors and entails the splitting of a singlet excited state into two lower triplet excitons located on adjacent ...chromophores. Research examining this phenomenon has recently seen a renaissance due to the potential to exploit singlet fission within the context of organic photovoltaics to prepare devices with the ability to circumvent the Shockley–Queisser limit. To date, high singlet fission yields have only been reported for crystalline or polycrystalline materials, suggesting that molecular disorder inhibits singlet fission. Here, we report the results of ultrafast transient absorption and time-resolved emission experiments performed on 5,12-diphenyl tetracene (DPT). Unlike tetracene, which tends to form polycrystalline films when vapor deposited, DPT’s pendant phenyl groups frustrate crystal growth, yielding amorphous films. Despite the high level of disorder in these films, we find that DPT exhibits a surprisingly high singlet fission yield, with 1.22 triplets being created per excited singlet. This triplet production occurs over two principal time scales, with ∼50% of the triplets appearing within 1 ps after photoexcitation followed by a slower phase of triplet growth over a few hundred picoseconds. To fit these kinetics, we have developed a model that assumes that due to molecular disorder, only a subset of DPT dimer pairs adopt configurations that promote fission. Singlet excitons directly excited at these sites can undergo fission rapidly, while singlet excitons created elsewhere in the film must diffuse to these sites to fission.
Despite their extremely low solubility in most solvents, hexagonal grey selenium and tellurium are shown to be remarkably soluble in binary mixtures of thiols and ethylenediamine (en) at room ...temperature and ambient pressure. A 1 : 4 vol/vol mixture of ethanethiol (EtSH) and en gave saturated solutions of 38 and 9.3 wt% for grey selenium and tellurium, respectively. Crystalline and phase-pure chalcogen is easily recovered from solution by drying and mild heat treatment at 250 degree C (for selenium) or evaporation at room temperature (for tellurium). To demonstrate utility for these dissolved chalcogens, it was shown that elemental antimony readily reacts with the dissolved selenium to give a stable, solution processable Sb-Se precursor solution. In the same way, elemental tin reacts with the dissolved tellurium to generate a Sn-Te precursor solution. Upon solution deposition and heat treatment to 250 degree C, these precursor solutions yielded crystalline Sb sub(2)Se sub(3) and SnTe.
The complexity of risks posed by climate change and possible adaptations for crop production has called for integrated assessment and modelling (IAM) approaches linking biophysical and economic ...models. This paper attempts to provide an overview of the present state of crop modelling to assess climate change risks to food production and to which extent crop models comply with IAM demands. Considerable progress has been made in modelling effects of climate variables, where crop models best satisfy IAM demands. Demands are partly satisfied for simulating commonly required assessment variables. However, progress on the number of simulated crops, uncertainty propagation related to model parameters and structure, adaptations and scaling are less advanced and lagging behind IAM demands. The limitations are considered substantial and apply to a different extent to all crop models. Overcoming these limitations will require joint efforts, and consideration of novel modelling approaches.
•Extreme events and future climate uncertainty represent risk for food production.•Crop models are largely able to simulate crop response to climate factors.•Adaptations are best evaluated in integrated assessment models (IAM).•Key limitations for crop models in IAM are low data availability and integration.•Cross-scale nature of IAM suggests novel modelling approaches are needed.
Crop models must be improved to account for the effects of heat stress events on crop yields. To date, most approaches in crop models use air temperature to define heat stress intensity as the ...cumulative sum of thermal times (TT) above a high temperature threshold during a sensitive period for yield formation. However, observational evidence indicates that crop canopy temperature better explains yield reductions associated with high temperature events than air temperature does. This study presents a canopy level energy balance using Monin–Obukhov Similarity Theory (MOST) with simplifications about the canopy resistance that render it suitable for application in crop models and other models of the plant environment. The model is evaluated for a uniform irrigated wheat canopy in Arizona and rainfed maize in Burkina Faso. No single variable regression relationships for key explanatory variables were found that were consistent across sowing dates to explain the deviation of canopy temperature from air temperature. Finally, thermal times determined with simulated canopy temperatures were able to reproduce thermal times calculated with observed canopy temperature, whereas those determined with air temperatures were not.
•Crop canopy temperature is needed to explain yield losses due to high temperatures.•A canopy level energy balance using Monin–Obukhov Similarity Theory (MOST) is presented.•Simplifications about the canopy resistance render it suitable for application in crop models.•The model is evaluated for a irrigated wheat canopy in Arizona and rainfed maize in Burkina Faso.
The UK food system is reliant on imported phosphorus (P) to meet food production demand, though inefficient use and poor stewardship means P is currently accumulating in agricultural soils, wasted or ...lost with detrimental impacts on aquatic environments. This study presents the results of a detailed P Substance Flow Analysis for the UK food system in 2018, developed in collaboration with industry and government, with the key objective of highlighting priority areas for system interventions to improve the sustainability and resilience of P use in the UK food system. In 2018 the UK food system imported 174.6 Gg P, producing food and exportable commodities containing 74.3 Gg P, a P efficiency of only 43%. Three key system hotspots for P inefficiency were identified: Agricultural soil surplus and accumulation (89.2 Gg P), loss to aquatic environments (26.2 Gg P), and waste disposal to landfill and construction (21.8 Gg P). Greatest soil P accumulation occurred in grassland agriculture (85% of total accumulation), driven by loadings of livestock manures. Waste water treatment (12.5 Gg P) and agriculture (8.38 Gg P) account for most P lost to water, and incineration ashes from food system waste (20.3 Gg P) accounted for nearly all P lost to landfill and construction. New strategies and policy to improve the handling and recovery of P from manures, biosolids and food system waste are therefore necessary to improve system P efficiency and reduce P accumulation and losses, though critically, only if they effectively replace imported mineral P fertilisers.
•Only 43% of imported UK food system phosphorus is converted into food and exportable commodities.•Manure P is a key driver of system surplus and inefficiency.•New policy to support a circular P economy is required.
Weather observations are essential for crop monitoring and forecasting but they are not always available and in some cases they have limited spatial representativeness. Thus, reanalyses represent an ...alternative source of information to be explored. In this study, we assess the feasibility of reanalysis-based crop monitoring and forecasting by using the system developed and maintained by the European Commission- Joint Research Centre, its gridded daily meteorological observations, the biased-corrected reanalysis AgMERRA and the ERA-Interim reanalysis. We focus on Europe and on two crops, wheat and maize, in the period 1980–2010 under potential and water-limited conditions.
In terms of inter-annual yield correlation at the country scale, the reanalysis-driven systems show a very good performance for both wheat and maize (with correlation values higher than 0.6 in almost all EU28 countries) when compared to the observations-driven system. However, significant yield biases affect both crops. All simulations show similar correlations with respect to the FAO reported yield time series.
These findings support the integration of reanalyses in current crop monitoring and forecasting systems and point to the emerging opportunities linked to the coming availability of higher-resolution reanalysis updated at near real time.
•Crop yield monitoring and forecasting systems driven by reanalysis show similar performance to the ones driven by weather observations.•Simulated wheat and maize yields are well correlated with FAO yields.•Significant biases in simulated wheat and maize yields still remain.
Abstract Objectives This study compared a behavioral weight loss program (BWL) with a stress management-based program, Emotional Brain Training (EBT), on weight loss, blood pressure, depression, ...perceived stress, diet, and physical activity. Methods Subjects with a body mass index (BMI) of >28 and <45 kg/m2 were recruited in Lexington, Kentucky in January 2014 and randomized to BWL or EBT for a 20-week intervention. Of those recruited, 49 participants were randomized to EBT or BWL. Randomization and allocation to group were performed using SPSS software. Weight, blood pressure, depression, perceived stress, dietary intake, and physical activity were measured at baseline, 10 week, and 20 week. Linear models for change over time were fit to calculate 95% confidence intervals of intervention effects. Results BWL produced greater changes in BMI than EBT at both 10 ( P = 0.02) and 20 wk ( P = 0.03). At 10 wk, both EBT and BWL improved BMI, systolic blood pressure, depression and perceived stress ( P < 0.05). BWL also improved diastolic blood pressure ( P = 0.005). At 20 wk, EBT maintained improvements in BMI, systolic blood pressure, depression, and perceived stress while BWL maintained improvements only in BMI and depression ( P < 0.05). Conclusions BWL produced greater weight loss than EBT; however, EBT produced sustained improvements in stress, depression, and systolic blood pressure. A combination of the two approaches should be explored.
Abstract Objective To examine changes in motivation and the relationship of motivation to adherence to self-monitoring and weight loss in a 16-week Internet behavioral weight-loss intervention. ...Design Two-group randomized design. Setting This study was conducted over the Internet. Participants Sixty-six women, ages 22-65, with a body mass index (BMI) between 25 and 40, and with a home computer with Internet access, participated. Intervention These data are from an Internet behavioral weight-loss program in which all participants received a face-to-face initial session followed by the 16-week Internet program. Main Outcome Measures Adherence to self-monitoring and weight loss were the main outcome measures. Analysis Linear regression and mediation analysis using the Baron and Kenny method were conducted. Results Autonomous motivation increased initially and remained high for those who ultimately achieved a 5% weight loss, but declined over time for participants who did not achieve a 5% weight loss. Autonomous motivation at 4 weeks was a predictor of adherence to self-monitoring and 16-week weight loss. Adherence mediated the relationship between autonomous motivation and weight loss. Conclusions and Implications These results suggest that autonomous motivation may be a promising intervention target for promoting program procedure adherence and weight loss.
Background: Diet quality plays an important role in health and has been shown to impact the risk of heart disease and certain cancers. The present study aimed to examine baseline and 16‐week ...follow‐up levels of energy intake, energy density and diet quality, as measured by the Healthy Eating Index 2005 (HEI‐2005), in overweight and obese women participating in a behavioural weight‐loss programme.
Methods: Sixty‐six women mean (SD) age 48.6 (10.8) years; body mass index 31.8 (3.7) kg m−2; 92% Caucasian completed dietary measures at baseline and follow‐up. All participants received a 16‐week Internet Behavioural weight‐loss programme based on the core of the Diabetes Prevention Program. Dietary intake was measured using the 2005 Block food frequency questionnaire. Diet quality was calculated using the HEI‐2005. Paired t‐tests were used to determine changes over time.
Results: There was a reduction in reported energy intake 7.867 (3.232) MJ versus 5.748 (1.775) MJ, P < 0.001 over the 16 weeks. Participants had an increase in diet quality HEI score = 53.9 (9.9) versus 57.4 (10.6), P = 0.002 as well as a reduction in energy density 0.0088 (0.0021) MJ g−1 to 0.0080 (0.0021) MJ g−1 (P = 0.002). All micronutrient intakes decreased over the 16 weeks.
Conclusions: Participation in a 16‐week behavioural weight‐loss programme significantly improved diet quality and reduced dietary energy density and energy intake in adult women. However, despite the overall increase in diet quality score, there were deficiencies in key micronutrients in the diets of most women at the conclusion of the 16‐week study.
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