Mechanical Efficiency Values Research Articles

Extraction of algae biodiesel for power generation and comparison of sustainable fuels using MCDM

ABSTRACT Current research talks about the extraction of green crude from algae using fast pyrolysis, comparison of properties of biofuel derived from various feedstocks, analysis of biofuels using multi-criteria decision-making (MCDM) method, performance on Variable Compression Ratio (VCR) engine. 2.11 mm2/sec (kinematic viscosity at 40°C) of biodiesel is cause ease in atomisation of fuel in engine and hence better thermal efficiency (η thb) and lower value of BSFC is observed. Analysis using MCDM proves algae biodiesel as best among the other feedstock. The fast pyrolyser is designed for the derivation of green crude from any feedstock. Response Surface Methodology (RSM) technique having a set of large numbers of runs is adapted to gain analytical results very close to the actual performance tests. The result for B0, B20, and B40 shows, the lowest value of BSFC of 0.34kg/kWh, the highest value of η thb = 27.59% and the highest value of mechanical efficiency = 48.56% are achieved at B20, with CR 17, the injection pressure of 200bar and at full load i.e. at 11 kg-f. Thus algae biodiesel as a cleaner and greener fuel is proven as a futuristic fuel for the automobile and power generation sector.

Factors Associated to Mechanical Efficiency among Adolescent Boys Performing a Graded Maximal Exercise

Factors Associated to Mechanical Efficiency among Adolescent Boys Performing a Graded Maximal Exercise Georges Jabbour1, Lina Majed1 1Qatar University, Doha, Qatar. PURPOSE: To determine the mechanical efficiency (ME) and associated factors among adolescent boys at different stages of graded maximal exercise. METHODS: 45 sedentary adolescent boys were separated into three groups according to their percentage of fat mass as follows: 15 normal-weight (NW) (body fat: 16.0 ± 1.9%), 15 overweight (OW) (body fat: 24.0 ± 1.6%) and 15 obese (OB) (body fat: 31.0 ± 3.0%). Each of them completed a maximal graded test in which energy consumption in watt (E), ME (expressed as a %), plasma epinephrine, and norepinephrine concentrations were determined consecutively through three stages corresponding to ~ 50% and 75% of each participant’s maximal heart rate (50%HRmax and 75%HRmax) and at peak oxygen consumption (VO2peak) level. RESULTS: During the maximal graded test, plasma epinephrine, and norepinephrine as well as ME determined at 50%HRmax, 75%HRmax and at VO2peak stages were significantly lower in OB compared to NW and OW individuals (ps<0.01). ME correlated negatively to body weight (r=-0.80; p<0.01) at 50%HRmax level. However, at 75%HRmax and at VO2peak stages, ME correlated significantly to power output (r=0.88 and r=0.91, ps<0.01) as well as with epinephrine (r=0.82, p<0.01) and norepinephrine concentrations (r=0.88, p<0.01) for entire group. CONCLUSION: These findings suggest that the body’s weight excess exerts a negative effect on ME values at a low intensity, while at higher intensities (75%HRmax and VO2peak) the lower ME could be better explained by the reduced catecholamine responses as observed in obese adolescent boys.

High-intensity interval training improves performance in young and older individuals by increasing mechanical efficiency.

This study evaluated the effects of 6 weeks of high‐intensity interval training (HIIT) on mechanical efficiency (ME) in young and older groups. Seventeen healthy young adults [26.2(2.4) year], and thirteen healthy older adults [54.5(2.3) year] completed a 6‐week HIIT intervention (three sessions per week) on an electromagnetically braked cycle ergometer. Each HIIT session contained six repetitions of supramaximal exercise intervals (6 seconds each) with 2 min of passive recovery between each repetition. ME (%) were computed in net terms across stages corresponding to ventilator thresholds 1 (VT1) and 2 (VT2) and at 100% of maximal oxygen consumption (VO 2max) of an incremental maximal cycling test. After 6 weeks, the ME values did not differ between the two groups and were significantly higher than the ones at baseline (P < 0.01). In this study, the multiple linear regression analysis demonstrated the increases in maximal power (Pmax) contributed significantly to ME increases over 6 weeks at VT1, VT2 and at 100% of VO 2max. This model accounted respectively for 28, 38, and 42%, of the increases. In older adults, ME determined during incremental maximal cycling test increases at VT1, VT2 and at 100% over 6‐week HIIT intervention, and the increment appeared to be related to increases in Pmax. HIIT can be recommended as a strategy aimed at improving muscle efficiency among older adults.

Thermodynamic and Mechanical Analysis of a Thermomagnetic Rotary Engine

A heat engine in magnetic system had three thermodynamic coordinates: magnetic intensity ℋ, total magnetization ℳ, and temperature T, where the first two of them are respectively analogous to that of gaseous system: pressure P and volume V. Consequently, Carnot cycle that constitutes the principle of a heat engine in gaseous system is also valid on that in magnetic system. A thermomagnetic rotary engine is one model of it that was designed in the form of a ferromagnetic wheel that can rotates because of magnetization change at Curie temperature. The study is aimed to describe the thermodynamic and mechanical analysis of a thermomagnetic rotary engine and calculate the efficiencies. In thermodynamic view, the ideal processes are isothermal demagnetization, adiabatic demagnetization, isothermal magnetization, and adiabatic magnetization. The values of thermodynamic efficiency depend on temperature difference between hot and cold reservoir. In mechanical view, a rotational work is determined through calculation of moment of inertia and average angular speed. The value of mechanical efficiency is calculated from ratio between rotational work and heat received by system. The study also obtains exergetic efficiency that states the performance quality of the engine.

Energy recovery by means of a radial piston expander in a CO2 refrigeration system

Natural refrigeration fluids as CO2 represent a very promising alternative to hydrofluorocarbons (HFCs) but they generally entail lower COP values. The possibility of recovering the large throttling losses by using an expander could give a substantial contribution to the performance improvement. In this work, a reciprocating expander developed from a hydraulic motor was experimentally analyzed. Despite of the mechanical losses due to the different original application of the machine, the thermodynamic cycles showed very promising results with the adoption of this solution. The machine isentropic efficiency was 19%, while the indicated efficiency was 66%, showing a very interesting potential of the expander. Thus, by considering a reasonable value of mechanical efficiency about 65%, the isentropic efficiency would be around 40%. Consequently, the entailed COP potential improvement, compared to a refrigeration system with simple throttling valve is currently at 7.4%, while it might overcome 20%.

Mechanical efficiency of high versus moderate intensity aerobic exercise in coronary heart disease patients: A randomized clinical trial.

Mechanical efficiency (ME) refers to the ability of an individual to transfer energy consumed by external work. A decreased ME, could represent an increased energy cost during exercise and may, therefore, be limited in terms of physical activity. This study aimed to compare the influence of two different exercise protocols: moderate continuous training (MCT) versus high intensity interval training (HIIT), as part of a cardiac rehabilitation program on ME values among coronary patients. One hundred and ten coronary patients were assigned to either HIIT or MCT groups for 8 weeks. Incremental exercise tests in a cycle ergometer were performed to obtain VO2peak. Net energy expenditure (EE) and ME were obtained at intensities corresponding to the first (VT1) and second (VT2) ventilatory thresholds, and at VO2peak. Both exercise programs significantly increase VO2peak with a higher increase in the HIIT group (2.96 ± 2.33 mL/kg/min vs. 3.88 ± 2.40 mL/kg/min, for patients of the MCT and HIIT groups, respectively, p < 0.001). The ME at VO2peak and VT2 only significantly increased in the HIIT group. At VT1, ME significantly increased in both groups, with a greater increase in the HIIT group (2.20 ± ± 6.25% vs. 5.52 ± 5.53%, for patients of the MCT and HIIT groups, respectively, p < 0.001). The application of HIIT to patients with chronic ischemic heart disease of low risk re- sulted in a greater improvement in VO2peak and in ME at VT1, than when MCT was applied. Moreover, only the application of HIIT brought about a significant increase in ME at VT2 and at VO2peak.

Course of Gross Mechanical Efficiency in Handrim Wheelchair Propulsion During Rehabilitation of People With Spinal Cord Injury: A Prospective Cohort Study

de Groot S, Dallmeijer AJ, Kilkens OJ, van Asbeck FW, Nene AV, Angenot EL, Post MW, van der Woude LH. Course of gross mechanical efficiency in handrim wheelchair propulsion during rehabilitation of people with spinal cord injury: a prospective cohort study. Objective To investigate the course of mechanical efficiency of handrim wheelchair propulsion during rehabilitation of subjects with (in)complete paraplegia and tetraplegia. Design Subjects were tested at the start of active rehabilitation (t 1), 3 months later (t 2), and when discharged from inpatient rehabilitation (t 3). They performed two 3-minute submaximal treadmill exercise blocks in a wheelchair. Setting Eight rehabilitation centers in the Netherlands. Participants Ninety-two people with (in)complete paraplegia and tetraplegia. Interventions Not applicable. Main Outcome Measures Mechanical efficiency values were calculated for each block. The course of mechanical efficiency was investigated using test occasions (t 1−t 3), completeness and level (paraplegia or tetraplegia) of the lesion, and power output as independent variables in a multilevel regression analysis. Results Mechanical efficiency significantly increased between t 1 and t 2 only. After adding level and completeness of the lesion and their interactions with time to the model, block 2 showed that subjects with paraplegia had a significantly higher mechanical efficiency than subjects with tetraplegia. Subjects with tetraplegia improved more between t 1 and t 2. Differences in mechanical efficiency between subjects with paraplegia and tetraplegia could not be explained by differences in absolute and relative power output levels. Conclusions Results showed a significant improvement in mechanical efficiency during the first 3 months of active rehabilitation. Subjects with paraplegia showed a higher mechanical efficiency than did subjects with tetraplegia, whereas the latter showed more improvement between t 1 and t 2.

Aerobic Energy Contribution during High Intensity Exercise

LANGUAGE NOTE | Document text in English; abstract also in Chinese.The review focuses on the aerobic energy contribution during high intensity cycling exercise. It is erroneous to assume that the energy demands of an exercise task can be met exclusively by either aerobic or anaerobic sources. During peak oxygen uptake determination, especially during the latter portions of the incremental exercise test, the anaerobic energy stores are also taxed. Not surprising, during maximal exercise of a short duration, there is also energy supplementation from aerobic energy sources. However, for a test to be considered predominantly anaerobic, the aerobic contribution to the test must be kept minimal. The quantification of aerobic contribution to a maximal exercise performance is difficult because the mechanical efficiency (ME) during a non-steady state exercise task remains speculative. Nevertheless extreme ME values for cycling have been proposed to provide a general scope of the estimated values. In adults, assumptions about oxygen uptake lag time, the size and role of the stored oxygen stores, which are taken into account also affect the magnitude to the aerobic contribution. Equivalent data on young people are insecure and greater research attention in this area is advised.本文著重介紹了大強度自行車運動中的有氧供能。如果認為運動中機體所需能量僅以某一能源系統，有氧系統或無氧系統供能是不正確的。在逐級遞增負荷測定最大攝氧量的運動中，尤其在測試的後階段，無氧系統參與供能。而在短時間的最大強度運動中，有氧供能也佔有一定的比例。即使進行無氧運動，在測試中仍能發現有低比例有氧供能。很難確定有氧系統在最大強度運動中的供能量為多少，因為不穩定狀態下的運動其供能效率仍不十分明確。但對於踏車運動中最高供能效率有一估計值範圍。對於成年人，攝氧量的延遲時間以及氧的儲存量的多少將影響最大有氧供能的比例。而在青少年中：有關這方面的資料較為缺乏，有待進一步的研究。

A stair-climbing test for ambulatory assessment of children with cerebral palsy.

The purpose of this study was to develop a stair-climbing test to measure energy cost (EC) and mechanical efficiency (ME) in children with cerebral palsy (CP) to evaluate ambulation-related motor function and its changes after intervention or maturation. Five normally developed (ND) and 10 children with CP were tested. The gross ME (MEg) was calculated from the work done (W) and the total energy cost (oxygen consumption) measured while repeatedly ascending and descending four steps for approximately 5 min without subtracting the resting metabolic rate. The MEg was significantly lower in CP than ND (3% versus 20%, P < 0.001). The test was repeated in the 10 children with CP after a 4-month therapy recess. The MEg values correlated with the initial tests, with a small, significant increase of 2%. When calculating net ME (MEn) from W and the energy cost above resting, the correlation of MEn values before and after therapy was inferior to that using MEg values. Similarly, individual ME values obtained by estimating energy cost from the increase in heart rate (HR) during stair-climbing also correlated poorly, with large variability. These results show that MEg may be used to evaluate changes in motor function resulting from age-related development or therapy. MEg is as good or superior to MEn; the extra time required to obtain resting energy cost and heart rate values is not necessary when measurements are desired within the same individual.

Prognostic value of mechanical efficiency in ambulatory patients with idiopathic dilated cardiomyopathy in sinus rhythm

ObjectivesThe purpose of this study was to determine, by analyzing the pressure-volume relationship, the prognostic value of parameters related to myocardial energetics for predicting mortality in patients with dilated cardiomyopathy (DCM) in sinus rhythm. BackgroundThe relationship between the myocardial energetics and the prognosis of patients with DCM in sinus rhythm remains unclear. MethodsWe followed 114 ambulatory patients with nonischemic DCM in sinus rhythm for a mean period of 5.8 ± 3.9 years. Over 70% of our patients were in New York Heart Association functional class I and class II. Pressure-volume data were obtained by the conductance method, and myocardial oxygen consumption per beat (Vo2) measurements were obtained. ResultsThe 3-, 5-, and 10-year cumulative survival rates were 88.6%, 80.0%, and 73.9%, respectively. Of the 114 patients, 47 were selected randomly to assess their myocardial energetics. By univariate analysis, the mechanical efficiency (ME, external work/Vo2), left ventricular (LV) ejection fraction and the LV end-diastolic pressure were statistically associated with cardiac death. The ME was the strongest predictor of survival in a Cox proportional-hazards analysis (p = 0.011). The best cutoff point of ME identified by the receiver-operating curve was 11%. This value had a sensitivity of 100%, a specificity of 87% and an overall predictive accuracy of 88% to distinguish survivors from nonsurvivors. ConclusionsThis study clearly demonstrates that ME is a powerful clinical predictor for cardiac death in patients with mild to moderate heart failure and with sinus rhythm. Whether these conclusions apply to patients with more severe heart failure requires further investigations.

Aerobic and anaerobic contribution to Wingate test performance in sprint and middle-distance runners

We investigated the aerobic and anaerobic contributions to performance during the Wingate test in sprint and middle-distance runners and whether they were related to the peak aerobic and anaerobic performances determined by two commonly used tests: the force-velocity test and an incremental aerobic exercise test. A group of 14 male competitive runners participated: 7 sprinters, aged 20.7 (SEM 1.3) years, competing in 50, 100 and 200-m events and 7 middle-distance runners, aged 20.0 (SEM 1.0) years, competing in 800, 1,000 and 1,500 m-events. The oxygen uptake (VO2) was recorded breath-by-breath during the test (30 s) and during the first 20 s of recovery. Blood samples for venous plasma lactate concentrations were drawn at rest before the start of the test and during the 20-min recovery period. During the Wingate test mean power (W) was determined and three values of mechanical efficiency, one individual and two arbitrary, 16% and 25%, were used to calculate the contributions of work by aerobic (Waer,ind,16%,25%) and anaerobic (Wan,ind,16%,25%) processes. Peak anaerobic power (Wan,peak) was estimated by the force-velocity test and maximal aerobic energy expenditure (Waer,peak) was determined during an incremental aerobic exercise test. During the Wingate test, the middle-distance runners had a significantly greater VO2 than the sprinters (P < 0.001), who had significantly greater venous plasma lactate concentrations (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Wheelchair propulsion efficiency

Low mechanical efficiency values in wheelchair propulsion are usually explained on the basis of the supply of force and power generated during the push phase. The purpose of this study is to analyze the movement and muscular activity pattern in handrim wheelchair propulsion, focusing on both the push and recovery phases. Data on cardiorespiratory and propulsion technique parameters were obtained from 40 wheelchair basketball players with extensive experience in wheelchair propulsion in six situations: two exercise levels (60% and 80% of individual VO2peak), and three velocities (1.11, 1.67, and 2.22 m.s-1) with constant power output on a treadmill. A two-factor analysis of variance with repeated measurements was applied with "exercise level" and "speed" as the main factors. A significant effect on gross mechanical efficiency was found when the velocity was increased from 1.67 to 2.22 m.s-1. Decreased mechanical efficiency could be explained by a significant change in the acceleration of the wheelchair-user system during recovery, caused by arm and trunk movements, inducing inertial forces to act on the wheelchair. Consequently, mechanical work increased significantly during the recovery phase. These findings indicate that studies on mechanical efficiency in wheelchair propulsion should not only be focussed on power supply during the push phase, but also on the movement pattern during recovery.

Physiological responses to maximal exercise on arm cranking and wheelchair ergometer with paraplegics

This study describes the responses of 20 paraplegic athletes (mean age: 26.8 +/- 1.6 years) to a continuous incremental workload test until exhaustion on an arm cranking ergometer (ACE) and on a wheelchair ergometer (WCE). Both ergometers used the same electromagnetic braking device allowing a fair comparison between results. Tests were conducted at a 24 hour interval at the same time of the day. Oxygen uptake (VO2), heart rate (HR), workload (W), blood pressure (BP), Borg index, and mechanical efficiency (ME) were measured at every minute during the effort and the cool down periods of both tests. The purpose of this study was to analyse the different responses obtained on ACE and on WCE during maximal effort by paraplegics, and also to determine which ergometer permits the higher ME. Results indicate that paraplegics reached the same max HR on ACE and on WCE (97% of the predicted max HR). The lack of significant difference (p less than 0.05) between ACE and WCE in terms of maximal values of VO2, VE and HR suggests that the subjects reached their maximal capacity on each test regardless of the type of ergometer. Nevertheless, W max (in Watts) was 26% higher on ACE than on WCE. Maximal ME values were respectively 16% and 11.6% on ACE and WCE. Results suggest that ergometers and protocol used in this study are appropriate to measure physiological responses of paraplegic athletes during arm cranking and wheelchair exercise without excessive or early arm fatigue.

Effects of power training on neuromuscular performance and mechanical efficiency

Effects of power training with stretch‐shortening cycle (SSC) exercises on mechanical efficiency (ME) were investigated with 9 young women who trained 3 times a week for 4 months. The training included various types of jumping exercises. Before and after the training as well as after the detraining (2 months) the subjects performed 6 different submaximal exercises with a special sledge apparatus. Each exercise involved 60 muscle actions lasting for a total of 3 min per testing condition. The work intensities were determined individually according to the recordings of distance obtained during the single maximal concentric exercises. The training caused the greatest changes of ME in conditions of higher prestretch intensities. The ME values changed from 49.3 ± 12.9% to 55.4 ± 12.1% in pure eccentric exercises and from 39.5 ± 4.6% to 46.1 ± 5.0% in SSC exercises during the training. After the training, the subjects preactivated their leg extensor muscles earlier before the impact, and the eccentric working phase was more powerful, because of higher tendomuscular stiffness. Higher preactivation of the measured muscles, higher flexion of knee and increased dorsiflexion of ankle joints in the beginning of contact caused the increased stiffness, possibly through more powerful reflex activation. At the same time the metabolic demands of muscles decreased, causing the increases of ME.

Art and the General Welfare

Our judgment of the level of civilization of any specific epoch in Western culture may well hinge upon the propositions which it takes for granted. That today one is forced to ask: Does art promote the general welfare? What, after all, does culture contribute to the common good or general enlightenment? indicates an aesthetic skepticism endemic to a narrowly pragmatic or commercial age, where the cash nexus reigns supreme and even the arts themselves have become corrupted by the values of mechanical efficiency and private profit. Le Corbusier thinks that a city street is a machine for traffic to pass through as efficiently as possible. Other urban architects are under the quaint delusion that a home is a housing project. And serious books are now written with the title Art as Investment to aid collectors whose collections perform the same role as portfolios of blue chip stocks and bonds. In other ages it was profoundly different. Cosimo de Medici, Sigismondo Malatesta, and Federigo da Montefeltro were also great collectors, and in some cases great businessmen, but they would have been scornful and contemptuous of a collector's passion guided by the principles of investment and tax deduction. The streets of the agora in Athens permitted rapid passage when necessary, but Alcibiades used them to meet and greet his friends, and Socrates lingered in them talking ethics and politics with sophists and young aristocrats as if they were a private club. And when Bess, Countess of Shrewsbury, commis-