Assessment of a low skeletal muscle mass (SM) is important for diagnosis of ageing and disease-associated sarcopenia and is hindered by heterogeneous methods and terminologies that lead to ...differences in diagnostic criteria among studies and even among consensus definitions. The aim of this review was to analyze and summarize previously published cut-offs for SM applied in clinical and research settings and to facilitate comparison of results between studies. Multiple published reference values for discrepant parameters of SM were identified from 64 studies and the underlying methodological assumptions and limitations are compared including different concepts for normalization of SM for body size and fat mass (FM). Single computed tomography or magnetic resonance imaging images and appendicular lean soft tissue by dual X-ray absorptiometry (DXA) or bioelectrical impedance analysis (BIA) are taken as a valid substitute of total SM because they show a high correlation with results from whole body imaging in cross-sectional and longitudinal analyses. However, the random error of these methods limits the applicability of these substitutes in the assessment of individual cases and together with the systematic error limits the accurate detection of changes in SM. Adverse effects of obesity on muscle quality and function may lead to an underestimation of sarcopenia in obesity and may justify normalization of SM for FM. In conclusion, results for SM can only be compared with reference values using the same method, BIA- or DXA-device and an appropriate reference population. Limitations of proxies for total SM as well as normalization of SM for FM are important content-related issues that need to be considered in longitudinal studies, populations with obesity or older subjects.
The nuclear cap-binding complex (CBC) stimulates processing reactions of capped RNAs, including their splicing, 3′-end formation, degradation, and transport. CBC effects are particular for individual ...RNA families, but how such selectivity is achieved remains elusive. Here, we analyze three main CBC partners known to impact different RNA species. ARS2 stimulates 3′-end formation/transcription termination of several transcript types, ZC3H18 stimulates degradation of a diverse set of RNAs, and PHAX functions in pre-small nuclear RNA/small nucleolar RNA (pre-snRNA/snoRNA) transport. Surprisingly, these proteins all bind capped RNAs without strong preferences for given transcripts, and their steady-state binding correlates poorly with their function. Despite this, PHAX and ZC3H18 compete for CBC binding and we demonstrate that this competitive binding is functionally relevant. We further show that CBC-containing complexes are short lived in vivo, and we therefore suggest that RNA fate involves the transient formation of mutually exclusive CBC complexes, which may only be consequential at particular checkpoints during RNA biogenesis.
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•PHAX and ZC3H18 compete for binding to the nuclear CBC•PHAX and ZC3H18 have opposite effects on the fate of snRNA precursors and other RNAs•PHAX, ARS2, and ZC3H18 bind capped RNAs without strong preference for given transcripts•CBC-containing complexes are short lived in vivo, with a lifetime of a few seconds
The nuclear CBC plays diverse roles in RNA biogenesis and it is not clear how selective effects are achieved for individual RNA families. Giacometti et al. suggest that RNA fate involves the formation of short-lived, mutually exclusive CBC complexes, which may only be consequential at particular checkpoints during RNA biogenesis.
The design of two heat pumps (HP), connected in series, was investigated for operation in the district heating (DH) network of the Greater Copenhagen area, Denmark. The installation was dimensioned ...to supply 7.2 MW of heat at a temperature of 85 °C. The heat pumps utilise a geothermal heat source at 73 °C. Both heat source and sink experience a large temperature change, which may lead to decreased performance for single vapour compression HP. The performance may be increased by using HPs connected in series and by applying HPs with zeotropic mixtures. First a generic study with a simple representation of the HP was applied to investigate optimal system configurations. It was shown that using two heat pumps in series with direct heat exchange in parallel with the first heat pump could increase the performance compared to the HP performance. Detailed thermodynamic models of a zeotropic mixture HP predicted that an exergetic efficiency of the units between 50% and 65% is possible. The technical feasibility as well as the economic viability of this installation was investigated for a range of optimal configurations. The analysis recommends a heat pump configuration with a system exergetic efficiency of 63%.
•Design of a geothermal heat pump system is suggested for district heat supply.•Connecting heat pumps in series and direct heat exchange is investigated.•The technical feasibility and economic viability is evaluated.•A feasible and viable solution is identified.
This paper compares estimation of the coefficient of performance (COP) of a large-scale heat pump (HP) for district heating based on four methods to the COP obtained using a detailed thermodynamic HP ...model. Four heat sources and varying district heating supply temperatures were considered. The COP estimation methods are based on constant COP, Lorenz efficiency, exergy efficiency and a method presented by Jensen et al. (2018). They were implemented in an energy planning tool and further analysed. The planning tool was used to assess HP implementation in a new district in Copenhagen, Denmark. The change in seasonal COP of the HPs, the economic results and optimal HP capacities were compared.
The results show that the Jensen et al. (2018) method provides good approximations and that the planning tool identifies a similar solution compared to the use of the thermodynamic HP model. Assuming a constant Lorenz efficiency, exergy efficiency or COP over the year resulted in large deviations in COP, especially for operations very different from the design conditions. Consequently, other heat sources were found for the most economical solution. The accuracy of the three methods decreased when the initial assumptions of constant COP and efficiencies differed from the ones at design conditions.
Background: A high amount of adipose tissue limits the accuracy of methods for body composition analysis in obesity. Objectives: The aim was to quantify and explain differences in fat-free mass (FFM) ...(as an index of skeletal muscle mass, SMM) measured with bioelectrical impedance analysis (BIA), dual energy X-ray absorptiometry (DXA), air displacement plethysmography (ADP), and deuterium dilution in comparison to multicompartment models, and to improve the results of BIA for obese subjects. Methods: In 175 healthy subjects (87 men and 88 women, BMI 20–43.3 kg/m 2 , 18–65 years), FFM measured by these methods was compared with results from a 3- (3C) and a 4-compartment (4C) model. FFM 4C was compared with SMM measured by magnetic resonance imaging. Results: BIA and DXA overestimated and ADP underestimated FFM in comparison to 3C and 4C models with increasing BMI (all p < 0.001). Differences were largest for DXA. In obesity, BIA results were improved: value corrected = value uncorrected – a(BMI – 30 kg/m 2 ), a = 0.256 for FFM and a = 0.298 for SMM. SMM accounts for 45% of FFM in women and 49% in men. Conclusions: In obesity, the use of FFM is limited by a systematic error of reference methods. In addition, SMM accounts for about 50% of FFM only. Corrected measurement of SMM by BIA can overcome these drawbacks.
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