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PubMed2002

Effects of power on perceived and objective group variability: evidence that more powerful groups are more variable.

The perception of group variability is affected by social power and status. Three different mechanisms may be responsible for these effects: (a) the power of the perceiver affects perceived group variability; (b) the power of the perceived group affects its perceived variability; and (c) the power of the group affects its actual variability. Two studies are reported to tease apart these three mechanisms and provide support for the third. In the first study, high- and low-power groups interacted and subsequently judged each other. In the second study, participants observed and rated the Study 1 groups, either knowing their power relationship or not. Results suggest that members of high-power groups manifest greater interpersonal variability than members of low-power groups.

Adult↗

PubMed1996

Variation in output power of laser prostatectomy fibers: a need for power measurements.

OBJECTIVES: The aim of this study was the assessment of the quality of side-firing fibers that are being used for laser prostatectomy, either by a laser light transmission measurement or by visual inspection. METHODS: A power meter (Aquarius) was developed to measure the actual power transmitted through a side-firing fiber and delivered to the prostatic tissue. The power measurements were performed under clinical conditions, that is, under water and at relatively high input power. Furthermore, a protocol was developed for visual inspection of the fibers. Eight types of side-firing fibers were measured before use. Before and after a procedure, three fiber types were measured: ProLase II (28 samples), UltraLine (23 samples), and UroLase (44 samples). All these fibers were used in standard treatment protocols. RESULTS: At 60 W the transmission of new fibers (not used) ranged between 49% and 83% when compared to a bare fiber. After use, a large variation was found in transmitted power between different samples of one device. A correlation with total transmitted power was not present. At higher power input, vapor bubbles are generated at the tip of the fibers. Depending on the fiber design, these bubbles have a major impact on the transmission. Only for the UroLase fiber was there a significant correlation between visual inspection and the transmission of used samples at 10, 20, and 40 W. CONCLUSIONS: The transmission strongly varies between fibers and between different samples of one fiber during clinical use. Moreover, the transmission does not correlate with visual inspection. A power measurement during a clinical treatment will contribute to a more controlled procedure and to a better comparison of clinical laser prostatectomy studies.

Biophysical Phenomena↗

PubMed2005

The power PC theory and causal powers: comment on Cheng (1997) and Novick and Cheng (2004).

It has been claimed that the power PC theory reconciles regularity and power theories of causal judgment by showing how contingency information is used for inferences about unobservable causal powers. Under the causal powers theory causal relations are understood as generative relations in which a causal power of one thing acts on a liability of another thing under some releasing condition. These 3 causal roles are implicit or explicit in all causal interpretations. The power PC theory therefore fails to reconcile power theories and regularity theories because it has a fundamentally different definition of power and does not accommodate the tripartite causal role distinction. Implications of this distinction are drawn out.

Cognition↗

PubMed1994

Determination of the relative linear collision stopping power and linear scattering power of electron bolus material.

The linear collision stopping power and linear scattering power for machineable wax relative to water have been determined for electron energies between 2 and 20 MeV. Knowledge of these quantities is necessary for the use of this wax as bolus in electron pencil-beam dose algorithms. The atomic composition of the wax (rho = 0.920 +/- 0.001 g cm(-3)) was obtained by having the wax assayed. The formalisms expressed in the ICRU Report 35 were used to calculate the relative linear collision stopping and linear scattering powers of the wax. The calculated relative linear collision stopping powers of 2 to 20 MeV electrons in the wax ranged from 0.949 +/- 0.005 to 0.952 +/- 0.005, and the calculated relative linear scattering powers ranged from 0.734 +/- 0.004 to 0.729 +/- 0.004. As a check of the calculation method, the relative linear collision stopping power was measured by determining the shift in electron central-axis depth-ionization curves when varying thicknesses of water were replaced by wax. These measurements, made using 10, 12, 15 and 18 MeV electron beams with wax thicknesses from 1.0 - 4.0 cm, resulted in a mean value of 0.931 +/- 0.008. Determination of the relative linear stopping power and the linear scattering power by using the measured CT number to extract values from patient data tables resulted in values of 0.933 +/- 0.009 and 0.746 +/- 0.016, respectively, indicating that it should be acceptable to use the Hounsfield values obtained with CT scans for treatment planning dose calculations.

Algorithms↗

PubMed1995

Comparison of thermocoagulation effects of low power, slow heating versus high power, rapid heating Nd: YAG laser regimens in a canine prostate model.

We compared the thermocoagulation effects of low power, slow heating (15 W x 180 seconds) versus high power, rapid heating (50 W x 60 seconds) laser regimens in the canine prostate. The study was performed in 20 mongrel canines. On each prostate, the low power regimen was delivered at the 2 and 4 o'clock positions, and the high power at the 8 and 10 o'clock positions. The laser power was measured at the fiber tip. Seven dogs (acute group) were sacrificed 1 hour after the procedure. The other 13 dogs (chronic group) were sacrificed at different time intervals from 3 days to 9 weeks after the procedure. The average depth of coagulation was significantly greater in lesions treated at low power (acute: 10.7 mm., chronic: 13.3 mm.) than in those treated at high power (acute: 8.5 mm., chronic: 11.6 mm.). Another potential benefit of the low power regimen observed in the study was preservation of the integrity and efficiency of the laser probe.

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↗

PubMed2004

Very low frequency power of heart rate variability is a powerful predictor of clinical prognosis in patients with congestive heart failure.

BACKGROUND: The present study examined whether the very low frequency (VLF) power of heart rate variability (HRV) is predictive of clinical prognosis in patients with congestive heart failure (CHF). METHOD AND RESULTS: The study recruited 54 consecutive CHF patients with emergency admission because of exacerbation of pulmonary congestion. Holter monitoring was performed after improvement of pulmonary congestion. The frequency components of HRV were calculated in the frequency domain (VLF, low frequency (LF), high frequency (HF), total power (TP) and the ratio of LF to HF power). The left ventricular ejection fraction was calculated, and plasma brain natriuretic peptide (BNP) and norepinephrine were also measured at discharge. Within a mean follow-up period of 19.8 +/- 11.7 months, 18 patients experienced cardiovascular events; 7 patients died and 11 patients required rehospitalization because of worsening of CHF. In univariate analysis, diabetes mellitus (DM), BNP and New York Heart Association (NYHA) functional class were significant as risk factors for cardiac events. VLF power, LF power and TP were the strong predictors for cardiac events in HRV. In multivariate analysis, VLF power predicted cardiac events independently of LF power, TP, DM, BNP and NYHA functional class (chi-square=6.24, p=0.01). CONCLUSIONS: VLF power is an independent risk predictor in patients with CHF.

Aged↗

PubMed2001

The load that maximizes the average mechanical power output during jump squats in power-trained athletes.

Three studies that used rugby league players experienced in power training methods as subjects were performed to investigate the resistance (percentage of 1 repetition maximum [1RM]) that maximized the average mechanical power output (Pmax) during the jump squat exercise. Maximum strength was assessed via 1RM (studies 2 and 3) or 3RM (study 1) during the full-squat exercise. Pmax was assessed during barbell jump squats, using resistances of 40, 60, 80, and 100 kg within the Plyometric Power System. All studies found that power output was maximized by resistances averaging circa 85-95 kg, representing 55-59% of 1RM full-squat strength. However, loads in the range of 47-63% of 1RM were often similarly effective in maximizing power output. The results of this investigation suggest that athletes specifically trained via both maximal strength and power training methods may generate their maximal power outputs at higher percentages of 1RM than those previously reported for solely strength-trained athletes and that there would appear to be an effective range of resistances for maximizing power output.

Adolescent↗

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↗

PubMed1993

Accounting for power: nurse teachers' and students' perceptions of power in their relationship.

In this paper I examine how nurse teachers and students perceive power to operate within their relationship. Interviews and focus group discussions showed that teachers and their students agreed that power operates within three distinct planes: the educational process, interpersonal relationships and learning outcomes. Common perceptions of power distributions within these planes were also demonstrated. A major difference was found to be in the emphasis accorded to power planes. Teachers related more to educational power while students were more concerned with personal power. I suggest how the findings can be applied to resolve seemingly conflicting teacher/student perceptions of power distribution and discuss how students believe they can best be empowered by teachers.

Adult↗

PubMed2005

Air quality impact of the coal-fired power plants in the northern passageway of the China West-East Power Transmission Project.

This paper analyzes the air quality impacts of coal-fired power plants in the northern passageway of the West-East Power Transmission Project in China. A three-layer Lagrangian model called ATMOS, was used to simulate the spatial distribution of incremental sulfur dioxide (SO2) and coarse particulate matter (PM10) concentrations under different emission control scenarios. In the year 2005, the emissions from planned power plants mainly affected the air quality of Shanxi, Shaanxi, the common boundary of Inner Mongolia and Shanxi, and the area around the boundary between Inner Mongolia and Ningxia. In these areas, the annually averaged incremental SO2 and PM10 concentrations exceed 2 and 2.5 microg/m3, respectively. The maximum increases of the annually averaged SO2 and PM10 concentrations are 8.3 and 7.2 microg/m3, respectively, which occur around Hancheng city, near the boundary of the Shaanxi and Shanxi provinces. After integrated control measures are considered, the maximum increases of annually averaged SO2 and PM10 concentrations fall to 4.9 and 4 microg/m3, respectively. In the year 2010, the areas affected by planned power plants are mainly North Shaanxi, North Ningxia, and Northwest Shanxi. The maximum increases of the annually averaged SO2 and PM10, concentrations are, respectively, 6.3 and 5.6 microg/m3, occurring in Northwest Shanxi, which decline to 4.4 and 4.1 microg/m3 after the control measures are implemented. The results showed that the proposed power plants mainly affect the air quality of the region where the power plants are built, with little impact on East China where the electricity will be used. The influences of planned power plants on air quality will be decreased greatly by implementing integrated control measures.

Air Pollutants↗

PubMed2002

Measuring corneal power for intraocular lens power calculation after refractive surgery. Comparison of methods.

PURPOSE: To find a more accurate and predictable method for intraocular lens (IOL) power calculation in eyes after refractive surgery. SETTING: Department of Ophthalmology, Kangnam St. Mary's Hospital, Seoul, Korea. METHODS: The accuracy of the following methods for calculating IOL power in 132 eyes after PRK or LASIK was compared: manual keratometry, hard contact lens, refraction-derived keratometry at the corneal plane, and the refraction-derived keratometry at the spectacle plane. Based on this comparison, the IOL power was calculated in the 2 eyes of a patient using refraction-derived keratometry at the spectacle plane with the SRK II formula. Cataract surgery with IOL implantation was then performed. RESULTS: The largest corneal power values were obtained using a manual keratometer and the smallest using refraction-derived keratometry at the spectacle plane (P <.001). In the patient having cataract surgery with IOL implantation, near target refraction was achieved with minimal error in IOL power. CONCLUSIONS: If the corneal power is known before refractive surgery, the use of the smallest value of those obtained using refraction-derived keratometry and the hard contact lens method is recommended. However, if the corneal power before refractive surgery is unknown, the use of the hard contact lens method is recommended.

Adult↗

PubMed2000

Peak power predicts performance power during an outdoor 16.1-km cycling time trial.

PURPOSE: To assess i) the reproducibility of peak power output recorded during a maximal aerobic power test (MAP), and ii) its validity to predict endurance performance during a field based 16.1-km time trial (16.1-km TT). METHODS: Two studies were completed: for part I, nine subjects performed three MAP tests; for part II, 16 subjects completed a MAP test and 16.1-km TT. Power output was recorded using an SRM power meter and was calculated as peak power output (PPO) recorded during 60 s of MAP and mean power output for the 16.1-km TT (16.1-km TT(PO)). RESULTS: There was no difference between PPO recorded during the three MAP trials, mean coefficient of variation for individual cyclists was 1.32% (95%CI = 0.97-2.03), and test-retest reliability expressed as an intraclass correlation coefficient was 0.99 (95%CI = 0.96-1.00). A highly significant relationship was found between PPO and 16.1-km TT(PO) (r = 0.99, P < 0.001) but not for PPO and 16.1-km TT time (r = 0.46. P > 0.05). CONCLUSION: The results show that PPO affords a valid and reliable measure of endurance performance which can be used to predict average power during a 16.1-km TT but not performance time.

Adult↗

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↗

PubMed2002

Synovial tissue of the hip at power Doppler US: correlation between vascularity and power Doppler US signal.

PURPOSE: To correlate power Doppler ultrasonographic (US) findings of the vascularity of synovial tissue of the hip joint with the results of histopathologic examination of the same tissue to assess the value of power Doppler US in the visualization of synovitis. MATERIALS AND METHODS: The hip joints of 24 patients with osteoarthritis (n = 15) or rheumatoid arthritis (n = 9) of the hip joint were examined with US before arthroplasty. The vascularity of the synovial membrane was classified qualitatively by using power Doppler US. During surgery, a section of the synovial tissue examined at power Doppler US preoperatively was resected. The vascularity of the tissue specimen was investigated and graded qualitatively by a pathologist who was not aware of the US findings. Visual qualitative grading was controlled by means of analysis of the US images and histopathologic specimens with a digital image evaluation system. Correlations between power Doppler US and histopathologic examination findings were calculated by using Spearman rank correlation and Pearson correlation tests. RESULTS: The correlation between the qualitative power Doppler US results and the qualitative vascularity grades was 0.92 (P <.01, Spearman rho). The correlation between quantitative and qualitative results was 0.93 (P <.01, Spearman rho) for US imaging and 0.97 (P <.01, Spearman rho) for histopathologic examination. CONCLUSION: Study results showed power Doppler US to be reliable for qualitative grading of the vascularity of synovial tissue of the hip.

Adult↗

PubMed2006

Adaptations in upper-body maximal strength and power output resulting from long-term resistance training in experienced strength-power athletes.

The purpose of this investigation was to observe changes in maximal upper-body strength and power and shifts in the load-power curve across a multiyear period in experienced resistance trainers. Twelve professional rugby league players who regularly performed combined maximal strength and power training were observed across a 4-year period with test data reported every 2 years (years 1998, 2000, and 2002). Upper-body strength was assessed by the 1 repetition maximum bench press and maximum power during bench press throws (BT Pmax) with various barbell resistances of 40-80 kg. During the initial testing, players also were identified as elite (n = 6) or subelite (n = 6), depending upon whether they participated in the elite first-division national league or second-division league. This subgrouping allowed for a comparison of the scope of changes dependent upon initial strength and training experience. The subelite group was significantly younger, less strong, and less powerful than the elite group, but no other difference existed in height or body mass in 1998. Across the 4-year period, significant increases in strength occurred for the group as a whole and larger increases were observed for the subelite than the elite group, verifying the limited scope that exists for strength gain in more experienced, elite resistance-trained athletes. A similar trend occurred for changes in BT Pmax. This long-term observation confirms that the rate of progress in strength and power development diminishes with increased strength levels and resistance training experience. Furthermore, it also indicates that strength and power can still be increased despite a high volume of concurrent resistance and endurance training.

Adaptation, Physiological↗

PubMed1997

Clinical and laboratory evaluation of powered electric toothbrushes: laboratory determination of relative interproximal cleaning efficiency of four powered toothbrushes.

The clinical brushing data from the paper entitled, Clinical and Laboratory Evaluation of Powered Electric Toothbrushes: In Vivo Determination of Average Force for Use of Manual and Powered Toothbrushes, by Boyd et al. in this Special Issue, were incorporated into a laboratory cleaning model. Utilizing a standardized brushing machine and a methyl methacrylate substrate, four powered brushing instruments were tested for cleaning efficiency: Rota-dent. Braun Oral-B. Interplak and Sonicare, and a manual toothbrush (Oral-B P40). The Sonicare powered brushing instrument was tested at the manufacturer's recommended brushing force of 0.5 N as well as a calculated force of 1.0 N. The results showed that the Rota-dent was more efficient (p < 0.01-0.001) in removing stain from both flat and interproximal surfaces than any of the other tested brushes. These results, together with those reported by McLey, et al. in Clinical and laboratory Evaluation of Powered Electric Toothbrushes: Laboratory Determination of Relative Abrasion of Three Powered Toothbrushes in this Special Issue, demonstrate that the rotary action Rota-dent instrument has the most efficient combination of low abrasion and high cleaning efficiency of the four powered brushes and the manual brush when all instruments were tested using clinically documented pressures.

Analysis of Variance↗

PubMedDate not supplied

Power generation from four skeletal muscle configurations. Design implications for a muscle powered cardiac assist device.

The development of long term cardiac assist devices is currently limited by the lack of an appropriate totally implantable power source. Transformed fatigue resistant skeletal muscle has been proposed as such a power source. The goal of this study was to determine the optimal latissimus dorsi muscle (LDM) configuration capable of obtaining maximum power output. Four separate in situ configurations were prepared: a latex compliance chamber placed between the LDM and chest wall (Sub-Dorsi), a chamber wrapped in a skeletal muscle ventricle (Circular), linear measurements from the thoracolumbar origin (Linear Origin), and linear measurements from the humeral insertion (Linear Insertion). A device was designed to measure the power output from each configuration in watts per kilogram of muscle. Eight LDMs were acutely studied at varying levels of pre-load. Performance characteristics were measured in each configuration. Peak power outputs were as follows: Sub-Dorsi: 8.3 +/- 1.6 W/kg at 50 cc or 11.6 N pre-load; Circular: 16.4 +/- 6.2 W/kg at 50 cc or 16.9 N; Linear Origin: 47.1 +/- 4.4 W/kg at 23.4 N; and Linear Insertion generated 59.9 +/- 12.1 W/kg at 26 N. Analysis of variance comparison revealed a significance of p < 0.0001. A linear oriented LDM is capable of generating maximal power output. Confirmation of these findings in transformed, conformed, fatigue resistant muscle will provide important performance information essential for the optimal design of implantable muscle powered ventricular assist systems.

Animals↗