SEARCH · PubMed Health

Results for “Power”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources

PubMed2001

The mechanical power output of the flight muscles of blue-breasted quail (Coturnix chinensis) during take-off.

Blue-breasted quail (Coturnix chinensis) were filmed during take-off flights. By tracking the position of the centre of mass of the bird in three dimensions, we were able to calculate the power required to increase the potential and kinetic energy. In addition, high-speed video recordings of the position of the wings over the course of the wing stroke, and morphological measurements, allowed us to calculate the aerodynamic and inertial power requirements. The total power output required from the pectoralis muscle was, on average, 390 W kg(-1), which was similar to the highest measurements made on bundles of muscle fibres in vitro (433 W kg(-1)), although for one individual a power output of 530 W kg(-1) was calculated. The majority of the power was required to increase the potential energy of the body. The power output of these muscles is the highest yet found for any muscle in repetitive contractions. We also calculated the power requirements during take-off flights in four other species in the family Phasianidae. Power output was found to be independent of body mass in this family. However, the precise scaling of burst power output within this group must await a better assessment of whether similar levels of performance were measured across the group. We extended our analysis to one species of hawk, several species of hummingbird and two species of bee. Remarkably, we concluded that, over a broad range of body size (0.0002-5 kg) and contractile frequency (5-186 Hz), the myofibrillar power output of flight muscles during short maximal bursts is very high (360-460 W kg(-1)) and shows very little scaling with body mass. The approximate constancy of power output means that the work output varies inversely with wingbeat frequency and reaches values of approximately 30-60 J kg(-1) in the largest species.

Animals↗

PubMed2005

Shared genetic and environmental effects on strength and power in older female twins.

PURPOSE: This study examined the relative contribution of genetic and environmental effects on maximal leg extensor power and also investigated whether leg extensor power and maximum voluntary isometric knee extensor strength share a genetic component. METHODS: Muscle functions were measured as part of the Finnish Twin Study on Aging in 101 monozygotic (MZ) and 116 dizygotic (DZ) female twin pairs aged 63-76 yr. Leg extensor power was measured using the Nottingham Leg Extensor Power Rig and maximum voluntary isometric knee extensor strength using an adjustable dynamometer chair. The analyses were carried out using the maximum likelihood method in Mx-program on the raw data set. RESULTS: A bivariate Cholesky decomposition model showed that leg extensor power and isometric knee extensor strength shared a genetic component in common, which accounted for 32% of the total variance in leg extensor power and 48% in isometric knee extensor strength. In addition, power and strength had a nonshared environmental effect in common accounting for four percent of the variance in power and 52% in strength. Remaining variance for leg extensor power was due to trait-specific shared and nonshared environmental effects. CONCLUSION: Observed genetic effect in common for leg extensor power and maximum voluntary isometric knee extensor strength indicated that these two traits are regulated by the same genes. However, also environmental effects have a significant role in explaining the variability in power and strength.

Aged↗

PubMed1996

Power Doppler sonographic pattern of acute pyelonephritis in children: comparison with CT.

OBJECTIVE: Focal areas of decreased perfusion may be shown by power Doppler sonography in children with acute pyelonephritis. The purposes of this study were to assess the ability of power Doppler sonography to reveal acute pyelonephritis and to compare the sonographic images with enhanced CT images. SUBJECTS AND METHODS: We performed B-mode sonography, power Doppler sonography, and enhanced CT (reference method) of the kidneys of 30 children with symptoms suggesting upper urinary tract infection. All imaging studies were obtained within 24 hr of admission of each child to our hospital. Power Doppler sonography was performed with the same equipment and the same settings for all children. Imaging studies were performed before the results of urine cultures were obtained. Triangular areas of decreased perfusion visible on both longitudinal and axial scans were considered indicative of acute pyelonephritis on power Doppler sonographic images. On CT images, areas of decreased attenuation of the renal parenchyma visible immediately after IV injection of iodinated contrast agent or areas of increased attenuation on delayed scans were considered indicative of acute pyelonephritis. Power Doppler sonography and CT were compared for each renal pole (n = 120). RESULTS: For 17 (89%) of the 19 patients with CT-proven acute pyelonephritis, power Doppler sonography diagnosed this condition on the correct side. Seventeen (77%) of the 22 poles showing acute pyelonephritis on CT scans were also revealed by power Doppler sonography. The two patients in whom acute pyelonephritis was not revealed by power Doppler sonography were an obese 15-year-old girl and a 7-year-old boy with right upper pole pyelonephritis. This boy was one of the first patients to be included in the study. Also, in an obese 11-year-old girl, a false-positive indication of pyelonephritis was given by power Doppler sonography. CONCLUSION: Power Doppler sonography seems to be significantly more sensitive than conventional sonography for the detection of acute pyelonephritis in children. This noninvasive technique should be able to replace CT or dimercaptosuccinic acid scintigraphy in many children with urinary tract infections.

Acute Disease↗

PubMed1986

Overcoming resistance to power sharing.

Power is a fundamental necessity for human development. Not only do people have a right to seek power, they have the duty to do so, if some force prevents them from pursuing their full development or promoting the development of persons dependent on them. Pope John Paul II, in his encyclical On Human Work, defends workers' right to seek power by forming unions to defend their vital interests and by striking if necessary. The bishops, through their pastoral letter on Catholic Social Teaching and the U.S. Economy, and the National Council of Churches in the United States also affirm this right. A refusal to share power usually means that the power holder perceives the purpose of power as "getting things done" rather than "helping people to grow." Resistance to power sharing can be attributed to three possible attitudes: Management's view that the sharing of power is a "gift" that can be withdrawn at any time; The perception of board members who come from the capitalist system that power sharing does not work; Adherence by management personnel in government to the theory that power holders' authority derives from the will of the people. Human service workers unquestionably can benefit from power sharing. The persons most in need of their services, however, also are powerless and must be considered in any discussion of a potential strike. Withholding services from these groups--the poor, minorities, children, the elderly, and the disabled--can result in a tragic tension, pitting the powerless against the powerless.

Catholicism↗

PubMedDate not supplied

Impact of CDMA wireless phone power output and puncture rate on hearing aid interference levels.

Interference between digital wireless phones and hearing aids occurs when the radiofrequency bursts from the phone transmission are demodulated by the hearing aid amplifier. The amplified interference signal is heard as a "buzz" or "static" by the hearing aid wearer. Most research and standards development activity has focused on worst-case scenarios with the phone operating at its maximum power. Since this power level is often not typical in urban and suburban settings, it is of value to determine the impact of lower power levels on the overall level of audible interference. Using a frequency analyzer, and several hearings aids and code division multiple access (CDMA) phones, the audio frequency spectrum of interference was recorded for each phone-aid combination and for a range of power levels producing from no interference to maximum interference. As phone power is increased, the interference signal becomes distinguishable from the ambient noise level and a linear response region is observed in which a specified increase in power output results in a proportional increase in the overall input referenced interference level (OIRIL). As power is increased beyond the linear region, the hearing aid enters a saturation region where an additional power increase results in a reduction or no increase in the OIRIL. The numeric differences in interference documented in this study were used in conjunction with the results of a previous study by the authors to determine the impact of reduced power on speech intelligibility and annoyance. The amount of improvement for a given power reduction depends on the radiofrequency immunity of the hearing aid and is substantial for hearing aids with poor immunity. For high-immunity aids, the level of audible interference remains low even at high phone power levels.

Equipment Design↗

PubMed2000

Theoretical evaluation of the distributed power dissipation in biological cells exposed to electric fields.

The paper deals with the power dissipation caused by exposure of biological cells to electric fields of various frequencies. With DC and sub-MHz AC frequencies, power dissipation in the cell membrane is of the same order of magnitude as in the external medium. At MHz and GHz frequencies, dielectric relaxation leads to dielectric power dissipation gradually increasing with frequency, and total power dissipation within the membrane rises significantly. Since such local increase can lead to considerable biochemical and biophysical changes within the membrane, especially at higher frequencies, the bulk treatment does not provide a complete picture of effects of an exposure. In this paper, we theoretically analyze the distribution of power dissipation as a function of field frequency. We first discuss conductive power dissipation generated by DC exposures. Then, we focus on AC fields; starting with the established first-order model, which includes only conductive power dissipation and is valid at sub-MHz frequencies, we enhance it in two steps. We first introduce the capacitive properties of the cytoplasm and the external medium to obtain a second-order model, which still includes only conductive power dissipation. Then we enhance this model further by accounting for dielectric relaxation effects, thereby introducing dielectric power dissipation. The calculations show that due to the latter component, in the MHz range the power dissipation within the membrane significantly exceeds the value in the external medium, while in the lower GHz range this effect is even more pronounced. This implies that even in exposures that do not cause a significant temperature rise at the macroscopic, whole-system level, the locally increased power dissipation in cell membranes could lead to various effects at the microscopic, single-cell level.

Animals↗

PubMed2004

Annual database of intraocular lens power in a Taiwanese population.

BACKGROUND: To derive a unique database of intraocular lens (IOL) power for Taiwanese, an ethnic group with a strikingly high prevalence of myopia. METHODS: A retrospective series of 3068 cases visiting Chang Gung Memorial Hospital, Linkou for cataract removal and posterior chamber IOL implantation between July 1999 and June 2000 was reviewed. The distribution of IOL powers and a possible age-correspondence was analyzed by one-way analysis of variance (ANOVA) test and multiple regression. RESULTS: Using the SRK/II linear regression formula, with an "A" constant of 118.5, the mean predicted IOL power required for emmetropia was 20.0 +/- 5.1 diopter (D). The mean IOL power for males was 19.8 +/- 5.1 D. The mean IOL power for females was 20.1 +/- 5.1 D. Moreover, ANOVA results documented a statistically significant tendency of age-dependence for IOL power distribution in the 3 groups (male, female, and male and female; F=24.53, p<0.05; F=16.39, p<0.05; F=40.54; p<0.05, respectively). In particular, it statistically significantly differed among decades over 40 years indicating that IOL power increased with age. However, the implanted IOL power decreased with age in patients younger than 40 years old. Multiple regression analysis showed that age, but not gender, was statistically significantly correlated to the IOL power distribution (p<0.05). CONCLUSION: We provide a unique database of IOL power for cataract surgeries in Taiwan. An age-related correspondence of the database of IOL powers was also documented in this study, which can therefore be regarded further cross-sectional evidence for the age-dependence prevalence of myopia.

Adult↗

PubMed2006

Effects of static stretching on leg power during cycling.

AIM: This study investigated the effects of warm-up involving static stretching on leg power. It was expected that the inclusion of static stretching in the warm-up would decrease leg power. METHODS: Twenty-seven healthy volunteers (16 male, 11 female) participated in the study. A prospective, repeated measures design was implemented where volunteers underwent 2 testing sessions at least 24 hours apart. One testing session involved a control warm-up (5 min submaximal cycling) followed by 4 10-s leg power tests at 5, 20, 40 and 60 min postwarm-up. For the other testing session, the subjects performed 5 min of submaximal cycling followed by 15 min of lower body static stretching and then the four leg power tests. Relative peak power, time to peak power and relative total work were measured for each leg power test. RESULTS: Peak power and total work were significantly greater after the static stretching warm-up compared to the control warm-up on all power tests. Peak power was achieved more quickly for the static stretching warm-up compared to the control warm-up on the 5 min test only. CONCLUSIONS: A warm up that includes static stretching has beneficial effects on anaerobic power events in comparison to submaximal cycling alone.

Adult↗

PubMed1977

Endoscopic laser treatment. II. Comparison of the efficacy of high and low power photocoagulation in control of severely bleeding experimental ulcers in dogs.

The coagulative efficacy of a "high power" argon laser which delivers 6.5 +/- 1.0 w was compared to that of a "low power" argon laser which delivers 1.0 +/- 0.1 w. The wave-guide angle of divergence was 8 degrees. For the high power laser, the distance between the wave-guide tip and the mucosa varied from 1.0 to 1.5 cm with a delivered power density range of 160 to 487 w per cm2. For the low power laser, the distance between the tip and mucosa varied from 0.7 to 1.3 cm with a power density of 35 to 146 w per cm2. Group A consisted of acute experiments in 6 heparinized dogs in which 51 standard-sized acute gastric ulcers extending into the submucosa were made at laparotomy via a large gastrotomy. Ulcer bleeding rates were quantified into three categories of severity. Within each category, ulcers were randomized to high power, low power, or untreated control. All 19 low power-treated ulcers and 16 untreated controls continued bleeding; 13 of 16 high power-treated ulcers stopped bleeding completely. Representative ulcers were examined histologically. Group B consisted of chronic experiments on 31 ulcers in 7 unheparinized dogs. These ulcers were either treated with high power or left as untreated controls. Dogs were killed and the ulcers were examined histologically at 7, 14, and 28 days. Only rarely did the laser injury penetrate into the muscularis externa. There were no perforations. By 14 days, all lesions were covered with normal surface epithelium. These data encourage further development of congruent to 7.0 w argon laser photocoagulation for eventual clinical use in man.

Animals↗

PubMed1987

Exercise endurance time as a function of percent maximal power production.

To develop and validate a mathematical model of the relationship between endurance time (T) and power production, 15 male subjects were first tested for maximal power on an instrumented cycle ergometer at 60 rpm. On subsequent days, they were tested for T at various percentages of maximal power. Curves of T as a function of percent maximal power were curvilinear, and could be made to overlap among subjects by individual abscissa scaling, which resulted in the appearance of horizontal stretching or compression of the curves. The degree of stretching-compression was defined by a statistically obtained scaling factor (F) which served to quantify each subject's endurance ability at fractions of maximal power. F was used to transform percent of maximal power to a scaled power variable (Psc). A curve of the form T = a(Psc)b was developed on 10 of the subjects and validated on the remaining five. Correlation between predicted and actual T was 0.967 for the fitting group and 0.980 for the validation group. A maximal power test and a single endurance test at 40 to 50% of maximal power were found to establish individual endurance-power curves fairly well, with a correlation of 0.828 between actual and predicted T. The combination of F and maximal power for a given physical activity provide a useful profile of an individual's ability to perform at constant exercise intensity.

Adult↗

PubMed1994

The accuracy of 'power' maps to display curvature data in corneal topography systems.

PURPOSE: To quantify the error introduced by videokeratographic corneal topography devices in using a paraxial formula to calculate power over the entire corneal surface, including areas removed from the central paraxial region where the formula is known to be invalid. METHODS: Corneal refractive power and two paraxial power approximations were computed as a function of distance from the apex for three theoretical surfaces, a sphere and two ellipsoids with 0.3 and 0.5 eccentricities. Color dioptric maps were then theoretically created. RESULTS: For the spherical surface, both curvature-based paraxial power approximations were uniform over the entire surface because curvature is constant. However, the corneal refractive power increased from center to periphery, demonstrating the known phenomenon of spherical aberration. For the ellipsoids, which have been shown to model the human cornea, curvature-based power approximations decreased from center to periphery because the curvature flattens peripherally. However, refractive power increased from center to periphery. The limits of the central paraxial region for these surfaces was shown to be approximately 2 mm in diameter for the paraxial power approximation used by videokeratographic devices to measure 8 mm in diameter. CONCLUSIONS: The direct correlation between corneal curvature and power with which clinicians are familiar is not valid in the peripheral regions measured by videokeratographic devices. Topographic devices measure curvature, which should not be interpreted as corneal power except in the central region. A recommendation to device manufacturers is to display "color curvature maps" instead of color dioptric maps, and to label the color bar with curvature values instead of power.

Cornea↗

PubMed1991

The constitution of physicians' power: a theoretical framework for comparative analysis.

Drawing on literatures documenting the experience of physicians in both European and American societies, a new theoretical framework for explaining variations in the professional power of physicians is provided. Most studies of professions have used professional organization as the principal explanatory variable, with state policy and the organization of civil society as secondary mediating factors. Our approach instead treats strategies of state power and forms of civil society as central features shaping the ability of the profession to exert power. Such a three-dimensional approach not only allows us to make more powerful classifications explaining contemporary differences, but also allows us to trace historical shifts and anticipate alternative futures in professional power. For example, in those societies where the state's intervention is limited and civil society is pluralistic, professional power is potentially greatest. But increasing state power does not necessarily reduce professional power. Where the state is most powerful and organizes all groups in civil society, professionals and society can be united in common struggle against the state. In response to that, it is likely that such centralized states will opt for corporatist solutions to maximize the internal differentiation of society and pit those once allied against one another, and preclude the organization of powerful autonomous interest groups.

Europe↗

PubMed2002

Relative power between sexual partners and condom use among adolescents.

PURPOSE: To examine how the relative power of adolescent sexual partners in the domain of emotional intimacy is related to condom use. METHODS: Interviewed 228 adolescents who visited an STD clinic in San Francisco. Adolescents were aged 14-19 years, 69% were female, and they were ethnically diverse. We developed a measure of relative power in the domain of emotional intimacy, by adapting five items from existing measures and developing three items ourselves. The partner who had less desire for emotional intimacy was considered to have more power in that domain. We also measured relative decision-making power. Data were analyzed using logistic regression and Student's t-tests. RESULTS: Adolescents who had more power than their partners in the domain of emotional intimacy were more likely to get their way about condom use than adolescents who had less power in this domain. Decision-making power was not related to whether adolescents got their way about condom use. Young men reported greater emotional intimacy power and greater decision-making power than young women. However, gender was not related to getting one's way about condom use. CONCLUSIONS: The results suggest the importance of assessing relative power in the sexual relationships of adolescents when predicting condom use.

Adolescent↗

PubMed2001

Power and self-perceived health in blind diabetic and nondiabetic individuals.

AIMS: The aims of this study were: (1) to explore perceptions of power in blind individuals and relate presence or absence of power to self-perceived health and (2) to compare self-perceived health in blind individuals with that of the general population. BACKGROUND: The theoretical framework of this study was Barrett's Power theory, which is based on The Rogerian nursing theory. Power is defined as being aware of what one is choosing to do, feeling free to doing it, and do it intentionally. METHODS: Thirty-nine blind subjects at three adjacent ophthalmology centres agreed to participate in the study. Of those 23 had become blind because of late complications of diabetes. Power was explored during semi-structured interviews and self-perceived health was measured with the Swedish health-related quality of life questionnaire. Data on socio-economic, rehabilitative and diabetes-related variables were also collected. FINDINGS: Power was experienced by 19 of the 39 respondents and was more frequently found in nondiabetic subjects than in diabetic subjects. Those experiencing power reported a better emotional and general health compared with individuals lacking power. The perception of having power was not significantly related to any other of the studied variables. When compared with age- and gender-matched controls from the general population, nondiabetic blind subjects scored higher in positive feelings and lower in physical functioning. In contrast diabetic subjects experienced poorer general health, less satisfaction with physical health and more negative feelings, but they reported that they did not experience limitation as a result of these emotions. CONCLUSION: One way of improving health in diabetic blind individuals could be to increase the subject's perception of power.

Activities of Daily Living↗

PubMed2006

Power and perspectives not taken.

Four experiments and a correlational study explored the relationship between power and perspective taking. In Experiment 1, participants primed with high power were more likely than those primed with low power to draw an E on their forehead in a self-oriented direction, demonstrating less of an inclination to spontaneously adopt another person's visual perspective. In Experiments 2a and 2b, high-power participants were less likely than low-power participants to take into account that other people did not possess their privileged knowledge, a result suggesting that power leads individuals to anchor too heavily on their own vantage point, insufficiently adjusting to others' perspectives. In Experiment 3, high-power participants were less accurate than control participants in determining other people's emotion expressions; these results suggest a power-induced impediment to experiencing empathy. An additional study found a negative relationship between individual difference measures of power and perspective taking. Across these studies, power was associated with a reduced tendency to comprehend how other people see, think, and feel.

Adult↗

PubMed1997

A personality disorder of excessive power strivings.

None of the existing formal diagnostic categories in psychiatry today addresses adequately the issues of excessive power-seeking, corruption and destructiveness. Excessive power strivings both poison the personality of the individual who is obsessed in his spirit and mind with power and do unacceptable harm to other peoples' lives. The present proposal of a diagnostic category of a Personality Disorder of Excessive Power Strivings is intended to fit into current diagnostic schema of DSM as well as into an earlier proposal (1) to examine in all psychopathology not only the burdens and damage people do and impose on their own selves and their own functioning, but also the harm they do to other peoples' lives and functioning. The diagnosis is to be used when the individual displays prolonged and severe manifestations of the following listed criteria: The basic feature which is always present in this personality disorder is: 1. Intense and extensive power strivings. In addition, at least three other of the following characteristics should be present; 2. Lack of empathy for people, and indifference to the suffering of others; 3. "Street smart" alertness and remarkable cunning committed to seizing and expanding power; 4. Ruthlessness in cultivation of power; 5. Scapegoating and projection of blame on to targeted individuals or a group, an insistent need to identify certain others as lowly, worthless and intended victims; 6. Corruption by power and addiction to power; 7. Demands of other people to be dependent on one's powerful personality, or that they become one's obedient followers; 8. Emphasis on symbolisms of pure vs. impure, holy vs. infidel, chosen vs. condemned; 9. A basic disrespect for the lives of others evidenced in callous or indifferent exposure of others to undue risks; 10. An absence of conscience in contexts of self-interest and opportunity; 11. A homicide/suicide orientation.

Antisocial Personality Disorder↗

PubMed1997

[Power in the hospital. Considerations on a structural problem].

This article tries to establish elements for an analysis of the power relations in hospital. After an explanation of the notion of power with recurrence to Max Weber, it presents different forms of the exercise of power. The traditional authoritarian form of power is compared with modern forms that are less personal and more anonymous. Then, the article tries to explain the special relationship between power and medicine. The basis for the analysis of this relationship is taken from Michel Foucault's analysis of power who describes medicine as the switch position of modern forms of exercise of power. He defines this under two different points of view: firstly, medicine works as an institution of disciplinary power, secondly, medicine is the sustainer of the bio-power, a kind of power that works by giving life.

Authoritarianism↗

PubMed1999

Evaluation of solid breast lesions with power Doppler sonography.

PURPOSE: We compared the abilities of power and conventional color Doppler sonography to depict the vascularity of solid breast lesions and evaluated the usefulness of power Doppler sonography in differentiating between benign and malignant breast lesions. METHODS: One hundred two solid breast lesions (59 benign and 43 malignant lesions) were studied with power and color Doppler sonography. Power and color Doppler sonograms were retrospectively compared for the depiction of blood flow signals. Power Doppler images were also reviewed for the amount of Doppler signals, pattern of vascularity, and morphology of vessels. The sensitivity, specificity, and accuracy of the 2 techniques were calculated. RESULTS: Compared with color Doppler sonography, power Doppler sonography depicted flow superiorly in 61 cases (60%) and equally in 41 cases (40%). On power Doppler sonography, the incidence of marked blood flow in malignant lesions (65%) was higher than that in benign lesions (39%). The pattern of vascularity was predominantly central (86%) and/or penetrating (65%) more often in malignant lesions than in benign lesions (51% and 34%, respectively). Branching (56%) and disordered vessels (42%) were seen more often in malignant lesions than in benign lesions (22% and 8%, respectively). The sensitivity, specificity, and accuracy in diagnosing malignancy were 64%, 76%, and 71%, respectively, for power Doppler sonography and 77%, 76%, and 76% for color Doppler sonography. CONCLUSIONS: Power Doppler sonography was more sensitive than color Doppler sonography in the detection of flow in solid breast lesions. Although power Doppler sonography was not more effective in diagnosing malignant lesions, central and penetrating vascularity patterns and branching and disordered vessels seem to be helpful findings in predicting malignancy.

Adolescent↗