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At least 19 recordsLinked to original sources

PubMed1985

The power to pollute and the power to preserve: perceptions of female power in a Hindu village.

In traditional Hindu village society, women are seen as having the power to pollute men. Such beliefs denigrate certain aspects of female sexuality. A detailed examination of these beliefs reveals that female sexuality is only associated with pollution and negative forces when women become estranged from men through their biology or other circumstances. When associated with pollution women are perceived as being in danger as well as endangering others. In contrast when women identify their interests with men's they are not in danger and can exercise positively valued powers such as the power to preserve life. The nexus of beliefs connected with female pollution and other mystical powers encourages women to subordinate their interests to men's.

Ethnicity↗

PubMed1990

Factors in maximal power production and in exercise endurance relative to maximal power.

The relationship of muscle fiber type and mass to maximal power production and the maintenance of power (endurance time to exhaustion) at 36%, 55%, and 73% of maximal power was investigated in 18 untrained but physically active men. Power output was determined at constant pedalling rate (60 rev.min-1) on a cycle ergometer instrumented with force transducers and interfaced with a computer. Maximal power was determined for each subject as the highest one-revolution average power. Fat-free mass was determined by hydrostatic weighing, fat-free thigh volume by water displacement and skinfold measurement, and percentage and area of type II fibers from biopsy specimens taken from the vastus lateralis. Maximal power averaged 771 +/- 149 W with a range of 527-1125 W. No significant correlations were found among percentage of type II fibers, relative area of type II fibers, or fat-free thigh volume and maximal power or endurance times to exhaustion at any percentage of maximal power. Weak but significant relationships were found for fat-free mass with both maximal power (r = 0.57) and endurance time at 73% of maximal power (r = -0.47). These results show maximal power to be more dependent on factors related to body size than muscle-fiber characteristics. The low correlations for so many of the relationships, however, suggest that individuals employ either different combinations of these factors or utilize other strategies for the generation of high power.

Ergonomics↗

PubMedDate not supplied

Increasing scientific power with statistical power.

A survey of basic ideas in statistical power analysis demonstrates the advantages and ease of using power analysis throughout the design, analysis, and interpretation of research. The power of a statistical test is the probability of rejecting the null hypothesis of the test. The traditional approach to power involves computation of only a single power value. The more general power curve allows examining the range of power determinants, which are sample size, population difference, and error variance, in traditional ANOVA. Power analysis can be useful not only in study planning, but also in the evaluation of existing research. An important application is in concluding that no scientifically important treatment difference exists. Choosing an appropriate power depends on: a) opportunity costs, b) ethical trade-offs, c) the size of effect considered important, d) the uncertainty of parameter estimates, and e) the analyst's preferences. Although precise rules seem inappropriate, several guidelines are defensible. First, the sensitivity of the power curve to particular characteristics of the study, such as the error variance, should be examined in any power analysis. Second, just as a small type I error rate should be demonstrated in order to declare a difference nonzero, a small type II error should be demonstrated in order to declare a difference zero. Third, when ethical and opportunity costs do not preclude it, power should be at least .84, and preferably greater than .90.

Data Interpretation, Statistical↗

PubMed1991

Statistical inference on mean dioptric power: asymmetric powers and singular covariance.

Methods have been developed recently for testing hypotheses on mean dioptric power and for constructing confidence regions in situations that are most likely to be encountered. In this paper the methods are extended to make the analysis complete. A new situation covered specifically is that of dioptric power not of the form sphere/cylinder x axis. Such powers, termed asymmetric powers because the dioptric power matrices are asymmetric, include the equivalent power of a thick obliquely crossed bitoric lens. A second situation is that in which the covariance matrix of the sample of powers is singular. Symmetric dioptric power (the more familiar form of power) can be represented by a point in three-dimensional space. In general, however, dioptric power is four dimensional in character. Singularity of covariance arises when variation in the sample is limited to a subspace of dimension less than the full three or four. The space spanned by the sample is called the range space of the sample. The dimension of the range space may be four, three, two, one or zero. Each case is considered in turn. Numerical examples of hypothesis testing are presented in range spaces of dimension four to one. The test statistic devised for each case also gives the equation of the confidence region about the mean of a sample of dioptric powers. Singularity can sometimes be avoided merely by taking larger samples and by taking more accurate readings. The problem of near singularity is briefly discussed. The paper allows basic hypothesis testing on mean dioptric power and the construction of confidence regions in all possible circumstances.

Multivariate Analysis↗

PubMed1975

Ventricular performance and energy of compression, power, and rate of change of power during isovolumic contraction.

During isovolumic contraction, there is a calculabe compression of the blood within the ventricle. Energy is expended by the ventricle during isovolumic contraction, and some of it is transferred to the blood in the form of elastic compression. The rate of energy transfer (power) and acceleration of energy transfer (rate of change of power) during isovolumic contraction were calculated based upon considerations of the energy of compression. In anaesthetized dogs, the isovolumic energy of compression was 42 plus or minus 6 (mean plus or minus SE) dyn cm; peak isovolumic power was 1,400 plus or minus 300 dyn cm sec-1; and peak rate of change of power was 56,000 plus or minus 15,000 dyn cm sec-2. During states of augmented contractility induced by isoproterenol, the peak acceleration of energy expeniditure (peak rate of change of power) increased to 126,000 plus or minus 33,000 dyn cm sec-2 (p smaller than 0.001). Conversely, with a reduction of contractility induced by propranolol, the peak isovolumic rate of change of power decreased to 30,000 plus or minus 5,700 dyn cm sec-2 (p smaller than 0.001). The peak rate of change of power was unaffected by changes of the afterload. A trend, however, suggests that it may be affected by preload. The derivations of the isovolumic energy of compression, power, and rate of change of power are based upon firm principles of fluid dynamics. No assumptions related to ventricular geometry, synergy of contraction, or characteristics of muscle fibers are implied. Because of its physiological meaning and the theoretical validity of its derivation, an expression such as the isovolumic peak rate of change of power, when utilized as an index of ventricular performance, would appear to be of value.

Animals↗

PubMed1975

The power struggle: definition and evaluation of power of muscular performance.

The authors define five different measurements of power of muscular performance. Using an isokinetic dynamometer, the velocity of motion is constant and thus can be controlled. Power, therefore, can be readily assessed. The speed of muscular contraction is of physiological and functional interest. The time it takes for muscles to develop force, the rate at which muscles can contract and sustain a force throughout the range of motion, and the relationship of speed to force are all facets of power. At least five terms which connote power of muscular performances are used today. These terms are power, peak power, average power, instantaneous power, and contractile power. The current misunderstanding of the terms and their misuses are discussed. Suggestions are offered for circumventing confusion in using power to describe motor performance.

Humans↗

PubMed1989

Comparison of maximum aerobic power, maximum anaerobic power, and skinfold thickness of elite and nonelite junior wrestlers.

The purpose of this investigation was to identify physiologic differences between elite high school-age wrestlers and nonelite wrestlers of comparable age, weight, and training experience. Two groups of junior wrestler, elite (n = 18) and nonelite (n = 18) were measured for maximum aerobic power (treadmill run), maximum anaerobic power of the arms and legs (Wingate test), and skinfold thickness. On the average (+/- SE) elite juniors had a VO2max of 52.6 +/- 2.0 ml/kg.min-1, 376 +/- 20 W for arm power, and 540 +/- 25 W for leg power. The nonelite group had a VO2max of 51.5 +/- 1.4 ml/kg.min-1 and 331 +/- 22 W and 467 +/- 29 W for arm and leg power, respectively. Ttests were computed to identify differences between the groups. The results revealed significant differences in four skinfold thicknesses, absolute anaerobic leg power, and relative anaerobic power of arms and legs. It was concluded that relative maximum anaerobic power is distinctly greater in elite high school wrestlers than less successful peers. In light of the results, it may be of benefit for wrestlers of lower caliber to decrease body fat, increase fat-free weight, and increase total body power through training.

Adolescent↗

PubMed1992

Output power and metabolic input power of skeletal muscle contracting linearly to compress a pouch in a mock circulatory system.

Output power and metabolic input power values were determined for unconditioned canine latissimus dorsi (two), gastrocnemius (seven), and triceps (three) muscles contracting linearly to cause compression of a doubly valved pouch in a hydraulic model of the circulation. The motor nerves to the muscles were stimulated tetanically with 450 msec trains of 0.1 msec pulses having a frequency of 50/sec. The muscles were contracted 10, 20, 30, and 40 times per minute and pouch output in milliliters per minute was measured directly for each muscle at each contraction (train) rate. The output power in milliwatts was determined by two methods: (1) by using the pouch output and the pressure rise imparted to the stroke volume (average power) and (2) by using the pressure-volume loop. Metabolic input power in milliwatts was determined from the oxygen consumption in milliliters per minute of the working muscle. It was found that as the pouch output was increased, the pouch output power and the metabolic input power both increased. The average power output was slightly less than that computed from the pressure-volume loop. The mean output power values, when pumping at L liters per minute, were 0.62 L (average) and 0.75 L mW/gm (pressure-volume loop) for the latissimus dorsi muscles; 0.83 L (average) and 1.16 L mW/gm (pressure-volume loop) for the gastrocnemius muscles; and 0.55 L (average) and 0.66 L mW/gm (pressure-volume loop) for the triceps muscles. The percent efficiency of energy conversion ranged from 9.2% to 17.8% for the latissimus dorsi muscles, from 5.1% to 19.5% for the gastrocnemius muscles, and from 10.5% to 27.3% for the triceps muscles. However, it should not be concluded that one muscle type is better than another on the basis of percent efficiency because efficiency does not take endurance into account. An important observation in this study relates to the large output obtained with the three linearly contracting muscle types. All were capable of pumping in excess of 1.5 L/min. A second observation relates to the absence of fatigue, although determination of endurance was not an objective in these studies.

Animals↗

PubMed1991

A comparison of median frequency, spectral edge frequency, a frequency band power ratio, total power, and dominance shift in the determination of depth of anesthesia.

Five numerical descriptors were derived from the electroencephalogram (EEG), recorded, and processed (Tracor Nomad) during emergence from isoflurane-nitrous oxide anesthesia. The five descriptors (median frequency, spectral edge frequency-90%, total power, a frequency band power ratio, and the ratio of frontal to occipital power) were compared for their ability to predict imminent arousal. Arousal was defined as spontaneous movement, coughing or eye opening. All of the descriptors except the frontal-occipital power ratio underwent significant (P less than 0.05) changes between the initial recordings made intraoperatively during surgical stimulus under anesthesia and later recordings in the 40 s preceding arousal. A post hoc analysis was performed to identify the threshold value for each parameter that best served to predict imminent arousal. For median frequency, spectral edge frequency-90%, total power, and the frequency band power ratio, thresholds that predicted imminent arousal with sensitivities of 90% and specificities of 82-90% could be identified. The data indicate that, even in the favorable circumstances of the present study (uniform anesthetic technique, post hoC identification of thresholds), none of several previously popularized EEG descriptors (median frequency, spectral edge frequency-90%, total power, a frequency band power ratio) can serve as a completely reliable sole predictor of imminent arousal. As presently derived, these EEG descriptors at best provide trend information to be used in concert with other clinical signs of depth of anesthesia.

Adult↗

PubMed1979

Uninterruptible power systems and other power protection equipment for electronic health care systems.

The increasing usage of electronic instruments in health care systems invariably leads to some level of dependence on them. In order to maximize the utility of these tools a high degree of reliability is essential. Many of the failures being experienced in systems where electronic instruments are being utilized may be attributed not to a failure of the instrument itself but rather to the poor quality of the commercial power to which they are attached. In order to reduce the effects of power fluctuations and outages, some type of power protection equipment must be installed between the commercial power system and the instrument. This article discusses the types of "electronic noise" present on commercial power lines and the various types of equipment used to reduce its effect on electronic instrumentation. In general, the Uninterruptible Power System (UPS) is shown to be the most effective power buffering element for a health care environment. General terminology associated with specifications of a UPS is defined in the article and attached appendix.

Electricity↗

PubMed1990

Elements of the dioptric power matrix and the concept of torsional power: a reinterpretation.

The elements of the dioptic power matrix have previously been interpreted in terms of power along particular meridians with the off-diagonal elements interpreted as a new form of dioptric power called torsional power. This paper shows that such new concepts are not necessary. Decomposition of the matrix provides an interpretation in terms that are quite familiar. The elements represent three component powers: the diagonal elements are two cylinders and the off-diagonal elements a crossed-cylinder with axes at 45 degrees and 135 degrees. The component crossed-cylinder obviates the need for the concept of torsional power. The concept of meridional power is avoided.

Mathematics↗

PubMed1988

Diluting power of thick limbs of Henle. III. Modulation of in vitro diluting power.

This paper considers the quantitative interplay of various factors in modulating diluting power of in vitro medullary and cortical thick ascending limbs of Henle (MTAL and CTAL, respectively) segments from mouse and rabbit. Experimentally, the measured diluting power of the in vitro rabbit CTAL is greater than that of the rabbit MTAL, although the inherent rate of net Cl- absorption at high perfusion rates is considerably greater in the rabbit MTAL than in the rabbit CTAL. Similar results apply when comparing the rabbit CTAL to the mouse MTAL exposed to antidiuretic hormone (ADH). Our calculations show that, in the rabbit CTAL, the measured static head luminal salt concentration can be accounted for quantitatively by the measured rate of net salt absorption at a high perfusion rate together with the passive permeability coefficients for Na+ and Cl-. Moreover, with perfusion rates of 10% of single-nephron glomerular filtration rate, the transport properties of the CTAL predict that, at the end of the CTAL, the static head luminal Cl- concentration occurs if the initial perfusate contains either 50 or 150 mM Cl-. Thus one can argue that, in vivo the CTAL may be the cardinal determinant of the TAL contribution to diluting power and to external salt balance. The relatively blunted diluting power of in vitro MTAL segments can be accounted for quantitatively by assuming that luminal dilution, and the attendant osmotic gradient from lumen to cell, suppresses the inherent rate of transcellular Cl- transport. Our calculations also show that prostaglandin E2 and peritubular osmolality increases blunt tubular diluting power. Thus in vivo, the MTAL segment may be the cardinal determinant of TAL contribution to concentrating power and to intrarenal salt balance.

Animals↗

PubMed1991

CO2 laser used through the operating channel of laser laparoscopes: in vitro study of power and power density losses.

The purpose of this study was to measure the effects of several variables on energy transmission and power density through the CO2 laser laparoscope. The factors studied included the laser beam diameter, coupler optics, laparoscope lumen size, and absorption of the laser wavelength by the insufflation gas. The addition of CO2 insufflating gas to the operating channel at higher power settings not only reduced the energy transmitted to tissue by 35-58% with a 7.2-mm laparoscopic operating channel and by as much as 61% with a 5-mm operating channel, but also increased the spot size. This "blooming" of the laser beam definitely reduced power density at tissue and eliminated the pinpoint spot size needed for microdissection. Even under optimal conditions regarding lumen size and beam diameter, our data indicate a point of diminishing returns for power density above 40 W for the systems tested. Power densities obtainable at laparotomy were not possible. Clinically, this effect resulted in optimal cutting (vaporization) at low power settings and coagulation accompanying cutting at higher settings.

Carbon Dioxide↗

PubMed1986

Power calculation in matched case-referent studies. Application and accuracy of the asymptotic power function.

Although the asymptotic power function for matched case-referent (case-control) studies has been given, it is not widely applied. One reason for this is that the parameters in the power function do not correspond directly to the usual description of the research situation. When designing a matched case-referent study, the potentially available relevant information concerns the joint distribution of the determinant and matching variate, and the illness rate in relation to those factors, in the study base. Application of the asymptotic power function using these inputs is described. The asymptotic power function is then assessed by use of the Monte Carlo method and is found to be accurate. An example of the application of the asymptotic power function is given.

Epidemiologic Methods↗

PubMed1990

[A power spectral analysis of the EEG in the newborns. II. The power spectral changes of the infants with neonatal asphyxia].

Power spectral analysis of the EEG at the neonatal period was performed in 33 babies with an Apgar score of 6 or less 1 minute after delivery. Their gestational ages ranged from 27 to 40 weeks, and birth weight from 1,013 g to 4,416 g. They were followed up until 18 months of age. All EEGs were recorded when the babies reached to 37-41 weeks of conceptional age, and analyzed using fast Fourier transformation. The percent power in active sleep was evaluated in this study. The abnormal EEG patterns in infants with neurological damage was classified into the following groups: (1) Increase of the percent power of the delta 1 band, (2) Decrease of the percent of the power of the delta 1. On the other hand, the EEG patterns at the neonatal period in infants with normal development who suffered from neonatal asphyxia were similar to those of age-matched controls. These results suggest one of the most important factors deciding the prognosis of the brain damage is the presence of a normal percent pattern. In conclusion, power spectral analysis of EEG at the neonatal period is useful in predicting the outcome of brain damage if it is used with visual inspection.

Asphyxia Neonatorum↗

PubMedDate not supplied

Hybrid-powered wheelchair: a combination of arm force and electrical power for propelling a wheelchair.

Many of the handicapped who could use a hand-driven wheelchair do not have sufficient arm force, arm movement and/or endurance for proper propulsion. Furthermore, there are users of electric wheelchairs who still have some arm functions and strength. In some cases a hand-driven chair, which can be propelled with reduced arm power, could be a better solution. By means of simulation, a study has been carried out to investigate the possibility of propelling a wheelchair by means of hybrid powering. Hybrid powering can be defined as a combination of arm force and electrical power. Using this hybrid principle, the necessary arm force can be decreased.

Arm↗

PubMed1992

Relation between meridional power and the dioptric power matrix.

The components of meridional power in any meridian can be expressed elegantly in terms of the dioptric power matrix. The form of the expressions is that which is well known in the statistical literature as a quadratic form; there are important statistical implications for dioptric power and its measurement. The relation forms the basis of the calculation and least-squares estimation of dioptric power and surface curvature from meridional measurements.

Humans↗

PubMed1978

The power motive, n power, and fear of weakness.

Among 85 male undergraduates, high need for power as measured by the 1968 Winter scoring system is shown to relate to high drinking frequency (p less than .01), high alcohol consumption (p less than .05), and taking the first drink at age 16 or less (p less than .05); to the Disinhibition ("Swinger") factor on Zuckerman's Sensation Seeking Scale (p less than .05) to poor academic performance (p less than .05); and to generate a regression equation with the California Psychological Inventory that suggests qualities of personal disorderliness and intellectual aggression. These findings, considered in terms of power motive theory, are seen as replicating earlier evidence that high n Power is maladaptie, voyeuristic and power avoidant.

Achievement↗