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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↗

PubMed2006

Generation of Cherenkov superradiance pulses with a peak power exceeding the power of the driving short electron beam.

Theoretical investigation of a short electron beam (extended bunch) interaction with a backward wave propagating in a slow wave structure demonstrates the possibility of producing ultrashort superradiance pulses with a peak power which exceeds the power of the driving beam (conversion factor K>1). It is shown that a nonuniform slow wave structure with optimized profile is beneficial in order to increase the conversion factor. The results of theoretical analysis are confirmed by the experiments. At X band using the SINUS-150 accelerator (4 ns, 330 kV, 2.6 kA) 0.6-0.8 ns superradiance pulses with a peak power of 1.2 GW and a conversion factor of 1.5 were obtained. Similar experiments at Ka-band based on the RADAN-303 accelerator (1 ns, 290 kV, 2.5 kA) demonstrated production of the superradiance (SR) pulse with duration 200 ps and peak power about 1 GW (conversion factor of 1.4).

Journal Article↗

PubMed2001

Power-law behavior of power spectra in low Prandtl number Rayleigh-Bénard convection.

The origin of the power-law decay measured in the power spectra of low Prandtl number Rayleigh-Bénard convection near the onset of chaos is addressed using long time numerical simulations of the three-dimensional Boussinesq equations in cylindrical domains. The power law is found to arise from quasidiscontinuous changes in the slope of the time series of the heat transport associated with the nucleation of dislocation pairs and roll pinch-off events. For larger frequencies, the power spectra decay exponentially as expected for time continuous deterministic dynamics.

Journal Article↗

PubMed1999

Real-Time Contrast Echo Assessment of Myocardial Perfusion at Low Emission Power: First Experimental and Clinical Results Using Power Pulse Inversion Imaging.

Power pulse inversion (PPI) has been developed for echocontrast specific imaging in order to reduce destruction of microbubbles. The purpose of this study was to evaluate PPI for real-time contrast echocardiography. Therefore, in vitro studies in a physiological flow-phantom and clinical examinations in patients with coronary artery disease were performed. The in vitro rersults of this study indicate that PPI allows real-time imaging at low emission power and is almost nondestructive to contrast microbubbles of Definity. At this low emission power a strong linear relationship between the dosage of the contrast agent and the resulting PPI signal intensity was found (R = 0.998, p < 0.001). In the clinical examinations real-time imaging using low mechanical index PPI resulted in strong myocardial signals and a complete filling of the cavities indicating absence of bubble destruction. Most striking was the ability of PPI to display myocardial thickening and wall motion simultaneously with the assessment of myocardial contrast replenishment following ultrasound induced bubble destruction by high power frames. We conclude that PPI allows nondestructive contrast imaging both in experimental and clinical settings. Therefore, real-time imaging of myocardial perfusion and real-time assessment of contrast replenishment following ultrasound induced destruction of microbubbles is feasible. Moreover, PPI allows simultaneous assessment of perfusion and myocardial function.

Journal Article↗

PubMed1996

Sound-power collection by the auditory periphery of the mongolian gerbil Meriones unguiculatus. II. External-ear radiation impedance and power collection.

Acoustic power flow into the external and middle ear of the gerbil is computed from acoustic measurements and models of the external ear and used to predict the behavioral auditory threshold. The external-ear radiation impedance from the tympanic ring ZE measured in six gerbil ears with a calibrated acoustic source at frequencies from 10 Hz to 18 kHz is mass dominated below about 8 kHz, with a mean mass of 2720 kg/m4. ZE shows resonant behavior near 8 and 14 kHz. The frequency dependence of ZE is similar to that measured in cat, chinchilla, and models of the human external ear, but the mass and the resonant frequencies are higher. The power utilization ratio (PUR) computed from ZE and measurements of the middle-ear input impedance ZT presented previously [Ravicz et al., J. Acoust. Soc. Am. 92, 157-177 (1992)] suggests that appreciable power is transmitted to the middle ear only above 1.5 kHz. Mathematical external-ear models, consisting of tube segments and conical horns that include viscous and thermal losses, were developed from anatomical dimensions to match ZE over the entire frequency range of measurement. The radiation efficiency eta R computed from the models is near unity only above 12 kHz and falls to 10(-5) as frequency decreases to 10 Hz. Predictions of the mean pressure gain from an external diffuse sound field to the tympanic membrane resemble measurements in another gerbilline species. The effective area of the ear in a diffuse sound field at the tympanic membrane EATMDF computed from PUR and eta R approaches the anatomical area of the pinna opening, 71 mm2, above 1.5 kHz and the geometric limit of lambda 2 /4 pi determined by the wavelength lambda above 12 kHz but decreases sharply below 1.5 kHz to 0.002 mm2 at 10 Hz. The diffuse-field sound pressure required to deliver 5 x 10(-17) W to the middle ear between 10 Hz and 18 kHz resembles the behavioral auditory threshold [Ryan, J. Acoust. Soc. Am. 54, 1222-1226 (1976)]. This result supports the idea that the cochlea acts as a power detector at the auditory threshold.

Acoustics↗

PubMed1997

Normalizing fractional moving blood volume estimates with power Doppler US: defining a stable intravascular point with the cumulative power distribution function.

PURPOSE: To normalize the power Doppler ultrasound (US) signal to the expected signal from 100% blood in the calculation of a fractional moving blood volume estimate. MATERIALS AND METHODS: To locate the signal from flowing blood with a consistent backscatter coefficient, the authors estimated the knee of the cumulative Doppler power distribution function. They used a flow-tube phantom to test the use of this knee to locate a radial position that would fall into a region of high shear stress and minimal rouleaux formation. They also studied how well the method normalized fractional moving blood volume estimates of the right renal cortex in a volunteer when simulating different body habitus and in a group of six healthy volunteers to estimate variability. RESULTS: Over five flow velocities and over undersaturated to severely oversaturated receiver gains, the calculated flow-tube area was a mean 89% +/- 7 (+/- standard deviation) of a standard. In humans, the technique normalized the fractional moving blood volume estimates over an 8-dB receiver gain variation; the mean +/- standard deviation of fractional moving blood volume estimates for the six volunteers was 37.6% +/- 3.6. CONCLUSION: Vascularity estimates with power Doppler US are feasible with a normalization scheme based on the cumulative Doppler power distribution function.

Adult↗

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↗

PubMed2003

The curvature constant parameter of the power-duration curve for varied-power exercise.

INTRODUCTION: The tolerable duration (t) for high-intensity cycle ergometry bears a hyperbolic relationship to the power output (P) with an asymptote termed the critical power (CP), and a curvature constant (W') that is numerically equivalent to an amount of work that can be performed above CP. The physiological nature of W' has received little consideration compared with CP, e.g., whether the total amount of work above CP remains constant when the power actually changes during the high-intensity task. PURPOSE: The purpose of this study was to compare W' derived from the standard estimation method, consisting of several different constant-P tests, and the total amount of work above CP during an exhausting exercise bout using a variable-P protocol. METHODS: Eleven healthy male subjects (age: 21-40 yr) volunteered to participate in this study. Each initially performed four-to-six high-intensity square-wave exercise bouts for estimation of CP [mean (SD); 213.3 (22.4) W] and W' [12.68 (3.08) kJ]. The subjects subsequently performed two variable-P tests to the limit of tolerance. During the first part, P was 117% or 134% of CP for a duration that expended approximately half of W'. The work rate was then abruptly increased to 134% (UP protocol) or decreased to 117% (DOWN protocol) of CP for the second part. RESULTS: There were no significant differences between W' [12.68 (3.08) kJ] and the total amount of work above CP during the UP [12.14 (4.18) kJ] and DOWN [12.72 (4.05) kJ] protocols (P > 0.05). CONCLUSION: We conclude that the work equivalent of W' is not affected by power variations during exhausting cycle ergometry, at least in the P range of 100-134% of CP.

Adult↗

PubMed2004

1.6 W of single-mode output power from a novel power-scaling scheme for monolithic nonplanar ring lasers.

A novel monolithic ring laser with high potential for power scaling, the disk nonplanar ring oscillator, is presented. We achieved power scaling by reducing the pump-light-induced aberrations. The basic idea of our approach is to attach a thin Nd:YAG disk to an undoped nonplanar YAG ring resonator while the other side of the disk is mounted on a heat sink. First promising experiments have demonstrated a single-frequency cw output power of 1.6 W at 1.06 microm with a slope efficiency of 45%. Power scaling to several watts seems to be possible.

Journal Article↗

PubMed2005

Single-frequency, single-mode, plane-polarized ytterbium-doped fiber master oscillator power amplifier source with 264 W of output power.

We present a single-frequency, single-mode, plane-polarized ytterbium-doped all-fiber master oscillator power amplifier source at 1060 nm generating 264 W of continuous-wave output power. The final-stage amplifier operated with a high gain of 19 dB and a high conversion efficiency of 68%. There was no evidence of rollover from stimulated Brillouin scattering even at the highest output power, and the maximum output was limited only by the available pump power.

Journal Article↗

PubMedDate not supplied

Low power lasers in physical therapy: measurement of optical output power of devices.

This report outlines the most essential characteristics of low power lasers commonly used in physical medicine. The optical output power of two Helium-Neon (HeNe) lasers (CW scanner) and two collimated Infrared (IR) laser diodes was measured with a CoherentR Model 212 meter designed to measure output power and its power density. The energy of two collimated IR lasers was measured with a Laser Precision Energy Meter equipped with an RJP-735 probe. The difficulties arising from the large divergence of the laser beam in diode lasers and the importance of the scattering and absorption of laser beams are discussed. The criteria for the evaluation of the lasers as well as the essential parameters for an adequate characterization of laser therapy are given.

Aluminum↗

PubMed2002

More power to you: simple power calculations for treatment effects with one degree of freedom.

Although numerous computer programs for statistical power analysis are available, power is an under-used aspect of experimental analysis, perhaps because of the perceived difficulty of performing the necessary calculations or because existing computer software can be expensive or complicated to learn. For single-degree-of-freedom tests, however, it is possible to calculate power in a straightforward manner, using the t distribution. Because these calculations are based on t, they use easily understood and readily available quantities. These calculations can be performed with a desk calculator; we also present a simple-to-use program called MorePower that will perform the necessary calculations. The straightforward nature of the calculations potentially will enable more researchers to consider issues of power when planning and reporting their experiments.

Humans↗

PubMed2001

B-mode, power Doppler and contrast-enhanced power Doppler ultrasonography in the diagnosis of breast tumors.

PURPOSE: To investigate the role of B-mode and unenhanced and enhanced power Doppler ultrasonography (US) in differentiating solid breast lesions, and to find out whether morphologically different tumors differ in terms of vascularity. MATERIAL AND METHODS: Sixty-five lesions, indeterminate or suggestive of malignancy after mammography were prospectively examined with B-mode and unenhanced and enhanced power Doppler US. The lesions were classified as benign, indeterminate or malignant at B-mode, and as benign or malignant at power Doppler US. The results were compared to the histologic diagnoses. Vascularity was analyzed also quantitatively to find out whether threshold values for differential diagnostics could be set. RESULTS: The sensitivity, specificity, and overall accuracy of the morphologic evaluation were 100%, 10%, and 57%, respectively. Rounded lesions were more vascular than spiculated lesions, but vascular assessment was only helpful when it supported a benign morphology. In quantitative analysis, due to the overlap between the benign and malignant lesions, no threshold values could be set. CONCLUSION: Morphologic criteria were useful in characterizing malignant lesions, but the large proportion of indeterminate findings decreased the specificity of US. Neither unenhanced, nor enhanced power Doppler US was able to improve diagnostic accuracy.

Adult↗

PubMed1998

[Instantaneous power maxima and power spectrum maxima analysis of second heart sounds signals].

We employed the time-frequency analysis to the processing of the second heart sound signals and studied the time-frequency spectrum of the normal and abnormal second heart sound. According to the time marginal and frequency marginal, we made the instantaneous power maxima and power spectrum maxima of the second heart sounds, which were thought as the quantity index about physiology and pathology. The results showed that the time-frequency spectrum of the second heart sounds gave a whole comprehensive description to dynamic course of the signals. The instantaneous power maxima and power spectrum maxima contain the time varying information in the second heart sound.

Heart Sounds↗

PubMed1986

The South African Defence Force physical training programme. Part II. Effect of 1 year's military training on muscular strength, power, power-endurance, speed and flexibility.

The effect of the South African Defence Force (SADF) military training on recruits' muscular strength, power, power-endurance, speed and flexibility was investigated. In the entire study group, a significant enhancement by basic training was observed for the isokinetic muscular strength of the right elbow extensors alone (17% increase; P less than 0,05). Stratification of training responses on the basis of initial fitness levels revealed significant improvements with basic training for all measures of muscular strength, power, power-endurance and speed, but not flexibility, in the below-average fitness recruit. For all variables the training effect was transient and values documented on completion of 1 year's military training differed insignificantly from those recorded before conscription. In contrast, with the exception of elbow extensor muscular strength, fitness levels of the average and above-average recruits were not increased by basic training. While further research to assess physical requirements of various military work and emergency situations is needed to evaluate the desirability of this observed selective enhancement of recruit fitness levels during basic training, it is evident that greater emphasis should be placed on flexibility training, and physical conditioning after basic training.

Adolescent↗

PubMed2001

Assessing health benefits of controlling air pollution from power generation: the case of a lignite-fired power plant in Thailand.

The impact pathway approach (IPA) is used to estimate quantitatively the level of health effects caused by particulate matter (PM10) and sulfur dioxide (SO2) emission from a lignite-fired power plant located in the Mae Moh area in northern region of Thailand. Health benefits are then assessed by comparing the levels of estimated health impacts without and with the installation of the flue gas desulfurization (FGD) equipment. The US EPA industrial source complex model is used to model air pollution dispersion at the local scale, and the sector average limited mixing meso-scale model is used to model air pollution transport at the regional scale. The quantification of the health end points in physical terms is carried out using the dose-response functions established recently for the population in Bangkok, Thailand. Monetarization of these effects is based on the benefit transfer method with appropriate adjustment. Finally, it has been found that the installation of the FGD to control SO2 emission at Mae Moh significantly reduces adverse health effects not only on the population living near the power plant but also all over the country. A FGD unit installed at the 300-MW power unit can result, on average, in 16 fewer cases of acute mortality, 12 fewer cases of respiratory and cardiac hospital admissions, and almost 354,000 fewer days with acute respiratory symptoms annually. In monetary terms this benefit is equivalent to US $18.2 million (1995 prices) per annum. This benefit is much higher than the annualized investment and operation costs of FGD (US $7.4 million/yr).

Air Pollutants↗

PubMed2002

Herpesviruses: balance in power and powers imbalanced.

The first veterinary herpesvirus symposium, organized under the patronage of the European Society for Veterinary Virology (ESVV) and the Swiss Societies for Microbiology (SGM-SSM), was held at the University of Zurich, Switzerland, on 22nd and 23rd of March 2001. The congress was divided into six sessions. The first session was dedicated to introductory lectures towards the main topics of the symposium, namely pathogenesis, immune response, and gene therapy. Session 2 was committed to new insights into herpesvirus-related gene therapy and vaccination. Specific and general aspects of the immune response against herpesviruses were presented in session 3, while session 4 was dedicated to virus replication. Session 5 was dedicated to a variety of poster presentations. Finally, session 6 revealed new insight into the pathogenesis of different herpesviruses. The present article summarizes the contributions and draws a new view of the herpesviruses. The herpesviruses have apparently found a multi-dimensionally balanced position between the powers of "cytopathogenicity" and "tumorigenicity" on one hand and "immunogenicity" and "tolerogenicity" on the other hand. As long as the different powers stay in balance, no or little clinical disease may be expected in association with herpesvirus infections. However, unbalanced actions of those powers may lead to disease.

Animals↗

PubMedDate not supplied

The power issue: determination of KB or Ki from IC50. A closer look at the Cheng-Prusoff equation, the Schild plot and related power equations.

INTRODUCTION: The Cheng-Prusoff equation (1973) is often applied to the determination of equilibrium dissociation constant (KB) of a competitive antagonist when the IC50 value is available. The purpose of this study is to illustrate that the slope function (K) of an agonist concentration-response curve is critical to the determination of KB values. METHODS: The article describes new equations, which incorporate the slope function, consequently yielding more accurate estimation of KB values for antagonists, and tests them using simulated data. The value of KB was calculated according to the following new power equation: KB = IC50/(l + A(K)/Kp) = IC50/[l + (A/EC50)(K)], where IC50 is the concentration of the antagonist producing 50% inhibition, A is the concentration of the agonist against which the IC50 is being determined and KP is the apparent equilibrium dissociation constant of the agonist. RESULTS: The new equation is the same as the Cheng-Prusoff equation when the slope function K is exactly unity. Application of the equation avoids errors inherent in the use of the Cheng-Prusoff equation when the slope function of the agonist concentration-response curve deviates from unity. The new equation was applicable to slope functions less than, equal to or greater than unity. All inhibition curves have a negative slope function of 1, indicating that there is only one single receptor population even though different slope functions of agonist concentration-response curves are involved. The importance of the power function in the Schild plot is illustrated by using the equation: log (x(K) - 1) = log B - log KB, where x is the concentration ratio and B is the concentration of the antagonist. DISCUSSION: This investigation illustrates the application of six power equations for accurate estimation of KB values covering situations with different slope functions of the agonist concentration-response curves.

Binding, Competitive↗