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OBJECTIVE: The potential usefulness of a new color Doppler ultrasonography technique called color power angiography in imaging fetal anatomy is presented. STUDY DESIGN: An ultrasonography system set on color power angiography was used to image fetal anatomy. Perfusion of normal organs was compared, with several fetuses demonstrating pathologic disorders of these organ systems. Color power angiography was compared with standard color Doppler imaging. RESULTS: We were able to demonstrate detailed imaging of the fetal vasculature in the lung, kidney, and brain. Abnormal lung and renal anatomy could be visualized by the distinctive perfusion "footprint." Fetal movement compromised the ability of color power angiography to visualize these structures but could be overcome by judicious use of the cineloop and persistence functions. Color power angiography was found to be more sensitive to low-flow states than was Doppler imaging. CONCLUSION: Color power angiography, which is more sensitive to low-flow states than color Doppler imaging is, may be useful in the imaging of normal and abnormal fetal anatomic structures.
To determine the effects of cycling experience, fitness level, and power output on preferred and most economical cycling cadences: 1) the preferred cadence (PC) of 12 male cyclists, 10 male runners, and 10 less-trained male noncyclists was determined at 75, 100, 150, 200, and 250 W for cyclists and runners and 75, 100, 125, 150, and 175 W for the less-trained group; and 2) steady-state aerobic demand was determined at six cadences (50, 65, 80, 95, 110 rpm and PC) at 100, 150, and 200 W for cyclists and runners and 75, 100, and 150 W for less-trained subjects. Cyclists and runners (VO2max: 70.7 +/- 4.1 and 72.5 +/- 2.2 mL.kg-1.min-1, respectively) maintained PC between 90 and 100 rpm at all power outputs and both groups selected similar cadences at each power output. In contrast, the less-trained group (VO2max = 44.2 +/- 2.8 mL.kg-1.min-1) selected lower cadences at all common power outputs and reduced cadence from approximately 80 rpm at 75 W to 65 rpm at 175 W. The preferred cadences of all groups were significantly higher than their respective most economical cadences at all power outputs. Changes in power output had little effect on the most economical cadence, which was between 53.3 and 59.9 rpm, in all groups. It was concluded that cycling experience and minimization of aerobic demand are not critical determinants of PC in well-trained individuals. It was speculated that less-trained noncyclists, who cycled at a higher percentage of VO2max, may have selected lower PC to reduce aerobic demand.
PURPOSE: : The purpose of this article is to analyze the geometry and examine the implications of the error cells of purely spherical powers in symmetric dioptric power space. METHODS: : In the context of spherocylindrical data spherical data typically implies a cylindrical component that is less than some particular amount (often 0.125 D) in magnitude. This error or uncertainty in cylinder is over and above the error in sphere itself. The two components of error are used to define the error cells in symmetric dioptric power space. RESULTS: : Error cells of spherical powers are constructed and presented as stereopairs. They are also shown in relation to error cells of powers in general. CONCLUSIONS: : An understanding of error cells can help the researcher avoid pitfalls in the analysis of spherocylindrical data. Perhaps surprisingly, the error cells of spherical powers are not invariant under spherocylindrical transposition.
Ageing compromises locomotor capacity and is associated with an increased risk of falls. Several lines of evidence indicate that both changes in muscle mass and performance are causative. Most studies, however, do not discern between effects of ageing, sedentarism and comorbidity. The present study compares the age effects in muscle cross section, force and power in physically competent self-selected subjects of different age groups. A total of 169 women and 89 men between 18 and 88 years, without any disease, impairment or medication affecting the musculoskeletal system were enrolled in this study. Calf muscle cross-sectional area was assessed by computed tomography. Muscle force and power were assessed by jumping mechanography. No significant correlation between muscle cross section and age was found in the men. A weak correlation in the women disappeared after correction for height. Close correlations with age, however, were found for peak force and peak power. Correction for muscle cross section or body weight further increased these correlation coefficients, particularly for peak power specific to body weight (r = 0.81 in women and r = 0.86 in men). The non-sedentarian population investigated here depicted a reduction of >50% between the age of 20 and 80 without a reduction in muscle cross section. This suggests a crucial role for muscular power in the ageing process. Possibly, the jumping mechanography as a measurement of anti-gravitational power output is a promising extension of the chair-rising test, known to be predictive for immobilization and the risk of falls.
The present article reviews the concept of statistical power analysis for research designs in headache. First, we present a basic overview of the concepts of statistical hypothesis testing. Then we discuss the elements of power analysis and, where appropriate, we address conventions for power calculations. We offer, for public use, an applied power calculator for two applications that are often encountered in headache research. We intend to help headache researchers design trials with adequate statistical power by offering a conceptual overview and the power calculators. In closing, we briefly address the implications of the present trend toward reporting point estimates of effect sizes with confidence levels.
AIMS/BACKGROUND: A recent advancement in Doppler ultrasonography (US) is power Doppler for detecting low-velocity blood flow at the microvascular level with angle independence. The present study was performed to characterize the factors contributing to the power Doppler signals of hepatocellular carcinoma (HCC). METHOD: Correlation of Doppler signals of HCC in 114 patients with 178 HCC nodules was analyzed in relation to the findings of CT and angiography, tumor characteristics (size, echo pattern, and histological differentiation of tumor), viral markers and severity of liver disease. RESULTS: The sensitivity of power Doppler US was superior to that of CT and angiography (each p<0.05; McNemar's test). The detection rate of power Doppler signal was significantly higher in tumors with diameter > or =2 cm (vs <2 cm in diameter), and with low/mixed echo pattern (vs high echo appearance), and with moderately/poorly differentiated HCC (vs well-differentiated HCC). Univariate analysis revealed that echo pattern, tumor size and histological differentiation of HCC in addition to CT and angiographic findings were significant. Multivariate analysis showed that tumor size and differentiation were significant. CONCLUSION: These results indicate that tumor characteristics play an important role in power Doppler signals and that these could be assessed by the presence or absence of power Doppler signals.
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.
This article considers power in clinical psychology. It is argued that power is present at every level of clinical psychologists' practice and can be used positively and negatively. Drawing on organizational, ethical, psychological, and personal influences, a heuristic problem-solving model for the process of understanding and resolving power-related ethical dilemmas is proposed. It is contended that such a model provides a humane and systematic process of understanding and working through power-related ethical dilemmas. It is argued that resolving power-related ethical issues cannot be achieved through the statement of absolute values but rather requires a process of understanding, action, and review. The model is used to draw out implications for promoting ethical practice and preventing the abuse of power in clinical psychology.
1. The work loop approach was used to measure mechanical power output from an asynchronous flight muscle, the dorso-ventral muscle of the bumblebee Bombus terrestris. Measurements were made at the optimum muscle length for work output at 30 °C and at a muscle temperature (40 °C) and oscillatory frequency (141­173 Hz, depending on the size of the animal) characteristic of free flight. Oscillatory strain amplitude was adjusted to maximize power output. 2. There was much preparation-to-preparation variability in power output. Power output in the muscles with the highest values was slightly greater than 100 W kg-1. It is argued that there are many experimental factors which might reduce measured power output below that in the living bumblebee, and no obvious factors which might lead to overestimates of muscle power. The conclusion is that flight muscle in the intact bumblebee can produce at least 100 W kg-1.
PURPOSE: : Although manufacturers of bicycle power monitoring devices SRM and Power Tap (PT) claim accuracy to within 2.5%, there are limited scientific data available in support. The purpose of this investigation was to assess the accuracy of SRM and PT under different conditions. METHODS: : First, 19 SRM were calibrated, raced for 11 months, and retested using a dynamic CALRIG (50-1000 W at 100 rpm). Second, using the same procedure, five PT were repeat tested on alternate days. Third, the most accurate SRM and PT were tested for the influence of cadence (60, 80, 100, 120 rpm), temperature (8 and 21 degrees C) and time (1 h at ~300 W) on accuracy. Finally, the same SRM and PT were downloaded and compared after random cadence and gear surges using the CALRIG and on a training ride. RESULTS: : The mean error scores for SRM and PT factory calibration over a range of 50 - 1000 W were 2.3 +/- 4.9% and -2.5 +/- 0.5%, respectively. A second set of trials provided stable results for 15 calibrated SRM after 11 months (-0.8 +/- 1.7%), and follow-up testing of all PT units confirmed these findings (-2.7 +/- 0.1%). Accuracy for SRM and PT was not largely influenced by time and cadence; however, power output readings were noticeably influenced by temperature (5.2% for SRM and 8.4% for PT). During field trials, SRM average and max power were 4.8% and 7.3% lower, respectively, compared with PT. CONCLUSIONS: : When operated according to manufacturers instructions, both SRM and PT offer the coach, athlete, and sport scientist the ability to accurately monitor power output in the lab and the field. Calibration procedures matching performance tests (duration, power, cadence, and temperature) are, however, advised as the error associated with each unit may vary.
PURPOSE: The purpose of this investigation was to: 1) compare actual peak power (PPactual) to estimated values (PPest) derived from three different prediction equations (Sayers and Harman), 2) determine the ability of the prediction formulas to monitor change following 6 wk of plyometric training, and 3) generate a new regression model. METHODS: colon; Twenty college females (age = 20.1 +/- 1.6 yr; body mass = 65.9 +/- 8.9 kg) were randomly assigned to a control or intervention group. Pre- and posttest countermovement jump (CMJ) height and PPactual were determined simultaneously on a force platform. Body mass and maximal CMJ height were used to predict peak power. RESULTS: colon; All three PPest were significantly correlated 0.84-0.99) and post (r = 372.4 W) was significantly less to PPactual and to each other on pre (r = 0.88-0.99) tests. PPactual (2425.4 +/- 2920.8 +/- 482.6 W; CMJ = 2925.1 +/- 409.7 than PPest (Sayers: SJ = 473.0 W) but was not different from PPest (Harman: 2585.0 +/- 409.7 W). Posttests revealed similar differences between PPactual and PPest for the intervention group, however no significant differences were observed for the control group. Mean differences from pre and posttests did not differ within or between PPest. Regression analysis determined the formula: ppest = 65.1 x (jump height) + 25.8 x (body mass) - 1413.1 (R = 0.92; SEE = 120.8), which slightly determined (0.77%) peak power is compared with PPactual in our cross-validation sample (n = 7) CONCLUSIONS: colon; Changes in peak power is accurate using any of the regression equations; however, the new prediction formula and that of Harman seem to more precisely estimate peak power. Strict jumping technique along with simultaneous measurement of power and jump height should be used as the standard for comparison.
We describe a calibration system that measures the nonlinearity of optical fiber power meters (OFPMs) at a maximum power of 0.6 W and a minimum power of 0.2 mW at 1480 nm. The system is based on the triplet superposition method. This system measures the nonlinearity of OFPMs by using correction factors at different powers; the system is an important tool for characterizing OFPMs at high powers in the S band. The measurement uncertainties, typically better than 0.2%, k = 2, associated with the high-power nonlinearity system are also described.
We present a cladding-pumped single-frequency, single-mode erbium:ytterbium codoped fiber master-oscillator power amplifier source generating up to 151 W of continuous-wave output power at 1563 nm with 33% slope efficiency and 20 dB gain. This source was also tunable and had a stable operation range of 1546 to 1566 nm at an output power level in excess of 125 W. The doped fiber exploited a large-core design for improved power handling and mitigation of stimulated Brillouin scattering. There was no sign of having stimulated Brillouin scattering even at the highest power. Despite a large core (V = 12), the output beam was nearly diffraction limited (M2 = 1.1). The source showed slight rollover at over 100 W of output power because of the onset of emission from ytterbium, centered at 1060 nm.
The ergometer can be a versatile means of measurement if attachments are developed for special purposes or if attachment is developed for multi-uses. In this study, an ergometer attachment for the measurement of power was designed and the measurement of power and the maximum anaerobic power in swimming was tested. A rotation drum was attached to one pedal of an ergometer. The rotation of this drum was synchronized with the rotation of the pedal. One end of a wire for a traction by a swimmer was connected to the drum. The other end of the wire was attached to a belt around the waist of a swimmer. The swimmer swam at full strength, thus causing the drum to rotate. The rotational velocity of the drum was detected as voltage by a magnetic permanent motor and transformed to wire tractional velocity; this velocity was equal to swimming velocity. The wire tension (= load) was controlled by a load adjusting lever of the ergometer. This wire tension was equal to the load which was added to the swimmer. The power calculation was based on a curved regression equation approximated from the load and the velocity. This equation was shown as follows; (P + a) (v + b) = (P0 + a)b or its development (P + a)v = b(P0 - P) and provided that P: force or load, v: swimming velocity, P0: maximum tractional force, a and b: constants. This ergometer attachment made it possible to measure and evaluate the power and the maximum anaerobic power in swimming with ease and at low cost. Measurement and evaluation are easily performed using the system, which is just one example of the possible applications of the ergometer.
PURPOSE: The aim of this study was to evaluate changes of eye refraction, corneal power and lens power during growth in emmetropia, myopia and hyperopia. MATERIAL AND METHODS: We examined 183 children (363 eyes) aged 4 to 19 with emmetropia, myopia and hyperopia. All measurements were performed after cycloplegia with 1% tropicamidum. Total refraction and corneal power was examined with autokeratorefractometer. Then we used ultrasound biometer Ocuscan (Alcon, USA), to measure axial length of the eye. Lens power was calculated with use of SRK II formula. RESULTS AND CONCLUSIONS: Mean refractive error in whole group in the age of 4 was +2,86D and was gradually decreasing to reach OD in the age of 14. Between 4th and 14th years old, myopia increases slowly and then acceleration of this process was observed. In hyperopic eyes between 4th and 16th years old, refractive error decreases gradually and then stabilization was noted. Mean corneal power between 4th and 19th years old, decreased in emmetropia and myopia by 1.24D and 2.19D respectively, and increased by 0.38D in children with hyperopia. This changes took place before 10th years old. Mean lens power between 4th and 19th years old, decreased in emmetropia by 2.01 D, in myopia by 1.43D and in hyperopia by 1.78D. This changes took place before 12th years old.
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.
Ultrasound biometry was done for 400 cases of cataract. The posterior-chamber lens power was found to be 18.2 +/- 4.26 D; the corneal refractive power, 43.78 +/- 1.86 D; and the axial length of the globe, 23.57 +/- 1.57 mm. The correlation between the refractive power of the cornea and the axial length shows the following physiological mechanism: (1) in hypermetropia an increase in corneal refractive power occurs in parallel with an increase in axial length; (b) in myopia an increase in axial length is compensated by a decrease in corneal refractive power, with both of the aforementioned conditions aiming at achieving emmetropia; and (c) patients with axial myopia either react in the form of condition b (state of compensation) or show an increase in corneal refractive power in association with an increase in axial length (state of decompensation).