Assessment of railway ground vibration in urban area using in-situ transfer mobilities and simulated vehicle-track interaction

This article proposes an alternative approach to the well-known Federal Railroad Administration method to evaluate ground vibrations induced by the passing of railway vehicles. The originality lies on the excitation mechanisms that occur in urban areas. A common source of railway-induced ground vibrations is local defects (rail joints, switches, and turnouts) which cause large amplitude excitations at isolated locations along the track. To analyse such situations, a combined numerical-experimental study is developed, based on the use of numerical train/track results and experimental mobility transfer functions. The influence of building foundation type, vehicle, defect type, and size and location is evaluated through experimental data collected in Brussels (Belgium). The results show that it is possible to assess vibrations from light rapid transit systems in the presence of local rail defects and unknown soil conditions

A hybrid two-step approach for evaluating the impact of local rail defect on building vibration.

With the development of light rail transit in urban areas, the effect of railway vibrations on buildings and people inside buildings is a growing problem. In particular, urban transit commonly generates large vibration levels at rail discontinuities, and thus this paper presents a 2-stage numericalexperimental vibration prediction methodology. The first step is purely numerical and focuses on the vehicle-track dynamics by analysing the effect of local defects at the rail surface during train passage. A multibody vehicle model and a flexible two-dimensional track are coupled using Herzian contact theory, which includes the geometry of the studied defect. The results obtained capture the interaction between the railway vehicle and the track, which serves as input for the second step. The latter uses experimental source transfer mobilities obtained on-site. This offers a way to accurately evaluate the soil-structure interaction which occurs in a complex medium such as the ground in urban areas. Structural response is then calculated by combining the two approaches. An illustrative example is presented, where the effect of various rail defects in the tram Brussels network is analysed. It is shown that it is possible to quantify vibration levels on light rail transit lines, where tramway networks interact with local rail defects and where railway ground vibration are problematic

A Hybrid Numerical-Experimental Assessment of Railway Ground Vibration in Urban Area

A common source of railway-induced ground vibrations is local defects such as rail joints, switches, and turnouts which cause large amplitude excitations at isolated locations along the track. Moreover, the distance between railway networks (tram, metro) and neighboring buildings is relatively close in urban areas. To analyze such situations, a combined numerical-experimental study is developed in this paper. The numerical approach addresses vehicle-track dynamics by considering the effect of local defects at the rail surface when a tram passes. A multibody vehicle model and a flexible two-dimensional track are coupled, which faithfully capture the interaction between the railway vehicle and the track. Field experiments are undertaken to determine track-ground dynamics. These involve measuring single source transfer mobilities between soil or building, and the force generated at the rail head, at the location of a local defect. The influence of building type and location is evaluated through experimental data collected in Brussels (Belgium). The results show that it is possible to assess vibrations from light rapid transit systems, while considering local rail defects as potential sources of vibration, and/or the complex paths associated with vibration transmission

Acute dietary nitrate supplementation and exercise performance in COPD: a double-blind, placebo-controlled, randomised controlled pilot study

Background: Dietary nitrate supplementation can enhance exercise performance in healthy people, but it is not clear if it is beneficial in COPD. We investigated the hypotheses that acute nitrate dosing would improve exercise performance and reduce the oxygen cost of submaximal exercise in people with COPD.Methods: We performed a double-blind, placebo-controlled, cross-over single dose study. Subjects were randomised to consume either nitrate-rich beetroot juice (containing 12.9mmoles nitrate) or placebo (nitrate-depleted beetroot juice) 3 hours prior to endurance cycle ergometry, performed at 70% of maximal workload assessed by a prior incremental exercise test. After a minimum washout period of 7 days the protocol was repeated with the crossover beverage.Results: 21 subjects successfully completed the study (age 68±7years; BMI 25.2±5.5kg/m2; FEV1 percentage predicted 50.1±21.6%; peak VO2 18.0±5.9ml/min/kg). Resting diastolic blood pressure fell significantly with nitrate supplementation compared to placebo (-7±8mmHg nitrate vs. -1±8mmHg placebo; p = 0.008). Median endurance time did not differ significantly; nitrate 5.65 (3.90–10.40) minutes vs. placebo 6.40 (4.01–9.67) minutes (p = 0.50). However, isotime oxygen consumption (VO2) was lower following nitrate supplementation (16.6±6.0ml/min/kg nitrate vs. 17.2±6.0ml/min/kg placebo; p = 0.043), and consequently nitrate supplementation caused a significant lowering of the amplitude of the VO2-percentage isotime curve.Conclusions: Acute administration of oral nitrate did not enhance endurance exercise performance; however the observation that beetroot juice caused reduced oxygen consumption at isotime suggests that further investigation of this treatment approach is warranted, perhaps targeting a more hypoxic phenotype.Trial Registration: ISRCTN Registry ISRCTN6609913

Long-Term Consequences of Developmental Alcohol Exposure on Brain Structure and Function: Therapeutic Benefits of Physical Activity

Developmental alcohol exposure both early in life and during adolescence can have a devastating impact on normal brain structure and functioning, leading to behavioral and cognitive impairments that persist throughout the lifespan. This review discusses human work as well as animal models used to investigate the effect of alcohol exposure at various time points during development, as well as specific behavioral and neuroanatomical deficits caused by alcohol exposure. Further, cellular and molecular mediators contributing to these alcohol-induced changes are examined, such as neurotrophic factors and apoptotic markers. Next, this review seeks to support the use of aerobic exercise as a potential therapeutic intervention for alcohol-related impairments. To date, few interventions, behavioral or pharmacological, have been proven effective in mitigating some alcohol-related deficits. Exercise is a simple therapy that can be used across species and also across socioeconomic status. It has a profoundly positive influence on many measures of learning and neuroplasticity; in particular, those measures damaged by alcohol exposure. This review discusses current evidence that exercise may mitigate damage caused by developmental alcohol exposure and is a promising therapeutic target for future research and intervention strategies

Locomotor and diaphragm muscle fatigue in endurance athletes performing time-trials of different durations

Purpose: Fatigue in leg muscles might differ between running and cycling due to inherent differences in muscle activation patterns. Moreover, postural demand placed upon the diaphragm during running could augment the development of diaphragm fatigue. Methods: We investigated quadriceps and diaphragm fatigue in 11 runners and 11 cyclists (age: 29±5years; $\dot{V}$ O2,peak: 66.9±5.5mlmin−1kg−1) by assessing quadriceps twitch force (Q tw) and transdiaphragmatic twitch pressure (P di,tw) before and after 15- and 30-min time-trials (15TT, 30TT). Inspiratory muscle fatigue was also obtained after volitional normocapnic hyperpnoea (NH) where postural demand is negligible. We hypothesized that running and cycling would induce different patterns of fatigue and that runners would develop less respiratory muscle fatigue when performing NH. Results: The reduction in Q tw was greater in cyclists (32±6%) compared to runners (13±8%, p0.05). Conclusion: Different levels of leg muscle fatigue in runners and cyclists could in part be related to the specific muscle activation patterns including concentric contractions in both modalities but eccentric contractions in runners only. Diaphragm fatigue likely resulted from the large ventilatory load which is characteristic for both exercise modalities and which was higher in 15TTs than in 30TTs (+27%, p<0.01) while postural demand appears to be of less importance