Correction For Leakage Research Articles

The Rapid ASKAP Continuum Survey III: Spectra and Polarisation In Cutouts of Extragalactic Sources (SPICE-RACS) first data release

AbstractThe Australian SKA Pathfinder (ASKAP) radio telescope has carried out a survey of the entire Southern Sky at 887.5 MHz. The wide area, high angular resolution, and broad bandwidth provided by the low-band Rapid ASKAP Continuum Survey (RACS-low) allow the production of a next-generation rotation measure (RM) grid across the entire Southern Sky. Here we introduce this project as Spectral and Polarisation in Cutouts of Extragalactic sources from RACS (SPICE-RACS). In our first data release, we image 30 RACS-low fields in StokesI,Q,Uat 25$^{\prime\prime}$angular resolution, across 744–1032 MHz with 1 MHz spectral resolution. Using a bespoke, highly parallelised, software pipeline we are able to rapidly process wide-area spectro-polarimetric ASKAP observations. Notably, we use ‘postage stamp’ cutouts to assess the polarisation properties of 105912 radio components detected in total intensity. We find that our StokesQandUimages have anrmsnoise of$\sim$80$\unicode{x03BC}$Jy PSF$^{-1}$, and our correction for instrumental polarisation leakage allows us to characterise components with$\gtrsim$1% polarisation fraction over most of the field of view. We produce a broadband polarised radio component catalogue that contains 5818 RM measurements over an area of$\sim$1300 deg$^{2}$with an average error in RM of$1.6^{+1.1}_{-1.0}$rad m$^{-2}$, and an average linear polarisation fraction$3.4^{+3.0}_{-1.6}$%. We determine this subset of components using the conditions that the polarised signal-to-noise ratio is$>$8, the polarisation fraction is above our estimated polarised leakage, and the StokesIspectrum has a reliable model. Our catalogue provides an areal density of$4\pm2$RMs deg$^{-2}$; an increase of$\sim$4 times over the previous state-of-the-art (Taylor, Stil, Sunstrum 2009, ApJ, 702, 1230). Meaning that, having used just 3% of the RACS-low sky area, we have produced the 3rd largest RM catalogue to date. This catalogue has broad applications for studying astrophysical magnetic fields; notably revealing remarkable structure in the Galactic RM sky. We will explore this Galactic structure in a follow-up paper. We will also apply the techniques described here to produce an all-Southern-sky RM catalogue from RACS observations. Finally, we make our catalogue, spectra, images, and processing pipeline publicly available.

Study on the influence of sampling methods for measuring soil radon exhalation rates

Soil is the primary source of radon in the atmosphere, and soil radon exhalation rate (E) is a key indicator to evaluate the radon hazard in soil. Radon can also be used as a tracer to analyze atmospheric processes and monitor greenhouse gas emissions. Therefore, improving the accuracy of measuring E is significant for radon protection and radon pollution management as well as public health. In this study, three different sampling methods were compared to determine the most suitable sampling method for E measurement under different conditions. The results indicated that the closed-loop gas-flow method can be used to measure E and required correction for leakage and counterdiffusion; E was found to vary from 13.25 ± 1.44 to 30.46 ± 2.19 mBq·m−2 s−1. For the open-loop gas-flow method, a low sampling flow rate was selected, and the sampling flow rate derived from this experiment was less than 0.2 l min−1; E varied from 36.11 ± 0.99 to 52.67 ± 1.68 mBq·m−2 s−1. For the activated-carbon adsorption method, the counterdiffusion effect had a negligible influence on the measurement results, and the measurement error due to the uneven distribution of radon in the carbon layer could be eliminated by changing the waiting time for the measurement; the measurement showed E of about 23 mBq·m−2 s−1. Moreover, the influence of water absorption of the activated carbon on the measurement results should be considered, and the water absorption rate should be less than 9%. The obtained values will serve as a reference for the rapid and accurate measurement of E.

Improvement of remanent polarization of CeO2–HfO2 solid solution thin films on Si substrates by chemical solution deposition

CeO2–HfO2 solid solution thin films, Hf1−xCexO2, are fabricated on n+-Si(100) substrates by the chemical solution deposition method. The effects of the CeO2 content and annealing temperature on the structure and ferroelectric properties of Hf1−xCexO2 are studied. The structural properties are investigated by glancing incidence x-ray diffraction and high resolution transmission electron microscopy, while the chemical states are examined by x-ray photoelectron spectroscopy. The results reveal that the admixture of CeO2 could effectively induce the ferroelectric phase. For Hf0.85Ce0.15O2 fabricated at an annealing temperature of 800 °C, an enhanced remanent polarization (Pr) of ∼20 μC/cm2 (after correction for leakage and parasitics) could be attained. Moreover, Hf0.85Ce0.15O2 demonstrates good endurance behavior, that the polarization does not show obvious degradation over 1 × 109 bipolar switching cycles, at an electric field of 2.9 MV/cm and a frequency of 100 kHz. This work highlights the importance of CeO2–HfO2 solid solution films in HfO2-based ferroelectric thin films.

What a difference carbon leakage correction makes!

In this paper, we investigate the effect of carbon leakage correction when turning from a production-based to a consumption-based approach. We consider six different regulatory regimes. For calculating carbon leakage corrections, we employ the Leontief Inverse derived from WIOD input/output tables. To account for country-specific characteristics we use OECD data. As modelling technique, we apply a non-parametric productivity estimation approach (Data Envelopment Analysis) to calculate relative efficiency scores of countries’ environmental performance to take their heterogeneity into account. The results suggest that irrespective of the chosen policy regime, the correction for carbon leakage will always lead to a significant reduction of emissions. The average effect of leakage correction amounts to 37% less CO2 emissions.

Very large remanent polarization in ferroelectric Hf1-xZrxO2 grown on Ge substrates by plasma assisted atomic oxygen deposition

Plasma assisted atomic oxygen deposition was used to grow polycrystalline ferroelectric Hf1-xZrxO2 (x = 0.5–0.7) on technologically important (100) Germanium substrates showing sharp crystalline interfaces free of interfacial amorphous layers and strong evidence for the presence of a predominately orthorhombic phase. The electrical properties, evaluated using metal-ferroelectric-semiconductor (MFS) capacitors, show symmetric and robust ferroelectric hysteresis with weak or no wake-up effects. The MFS capacitors with x = 0.58 show very large remanent polarization up to 34.4 μC/cm2 or 30.6 μC/cm2 after correction for leakage and parasitics, combined with good endurance reaching 105 cycles at a cycling field of 2.3 MV/cm. The results show good prospects for the fabrication of Ge ferroelectric field effect transistors (FeFETs) for use in 1 T FeFET embedded nonvolatile memory cells with improved endurance.

Assessment of leakage dose in vivo in patients undergoing radiotherapy for breast cancer.

Background and purposeAccurate quantification of the relatively small radiation doses delivered to untargeted regions during breast irradiation in patients with breast cancer is of increasing clinical interest for the purpose of estimating long-term radiation-related risks. Out-of-field dose calculations from commercial planning systems however may be inaccurate which can impact estimates for long-term risks associated with treatment. This work compares calculated and measured dose out-of-field and explores the application of a correction for leakage radiation.Materials and methodsDose calculations of a Boltzmann transport equation solver, pencil beam-type, and superposition-type algorithms from a commercial treatment planning system (TPS) were compared with in vivo thermoluminescent dosimetry (TLD) measurements conducted out-of-field on the contralateral chest at points corresponding to the thyroid, axilla and contralateral breast of eleven patients undergoing tangential beam radiotherapy for breast cancer.ResultsOverall, the TPS was found to under-estimate doses at points distal to the radiation field edge with a modern linear Boltzmann transport equation solver providing the best estimates. Application of an additive correction for leakage (0.04% of central axis dose) improved correlation between the measured and calculated doses at points greater than 15 cm from the field edge.ConclusionsApplication of a correction for leakage doses within peripheral regions is feasible and could improve accuracy of TPS in estimating out-of-field doses in breast radiotherapy.

Bayesian Modelling of Kenya Extreme Debt with Correction for Budgetary Leakage

Total public debt levels in Kenya are exponentially increasing due to rising budget deficit, poor public fund management as well as movement of various macro-economic indicators such as balance of payments, inflation, Gross Domestic Product, exchange rates, and grants leading to worries on whether or not the high debt levels would be sustainable in future. The major concern is that a huge portion of the country’s revenue is committed to debt repayment and budgetary leakage strains the repayment efforts, thereby accelerating the country's debt unsustainability. This study sought to model extreme debt in Kenya with correction for budgetary leakage using a Bayesian approach to Extreme Value Theory (EVT) the main aim being to estimate the maximum debt tolerable for the country. A non-stationary Generalized Pareto Distribution (GPD) model is used for modeling the public debt extremes which depend on some covariates (macro-economic indicators) and Bayesian methods used to directly estimate the threshold and the GPD parameters. A major contribution of this study is the introduction of a compensator to allow for possible leakage due budgetary leakage through corruption, tax evasion, money laundering, and other forms of financial fraud, modelling it as a function of budget deficit. The established debt threshold is approximately KShs. 2 trillion which is the standard amount that should be borrowed, beyond which values are considered extremes. The results indicate that the movements in the macro-economic debt indicators significantly affect total public debt levels, and that budgetary leakage reduces Kenya's debt tolerance. The research concluded that the current debt level of around KShs. 5 trillion is still sustainable but high budgetary leakage may accelerate the country's long-run debt unsustainability. For further work, it is recommended to use a time-varying threshold to capture seasonality of the public debt series.

The MOTH II Doppler-Magnetographs and Data Calibration Pipeline

AbstractThe calibration pipeline of the level zero images obtained from the Magneto-Optical filters at Two Heights (MOTH II) instrument is presented. MOTH II consists of two 20 cm aperture instruments, each using a Magneto-Optical Filter (MOF): one at 5896 Å (Na D2-line), the other one at 7700 Å (K I-line). MOTH II instruments thus provide full disk line-of-sight Doppler velocity and magnetic field measurements at two heights in the solar atmosphere. The developed MOTH II pipeline employs a set of standard calibration corrections, a correction for signal leakage, due to the non-ideal behavior of the polarizers, and the geometrical registration between the eight images acquired by four CMOS cameras, relative to two components of the signal in two circular polarization states, in each of the two channels. MOTH II data are used to investigate atmospheric dynamics (e.g., internal gravity waves and magneto-acoustic portals) and Space Weather phenomena. Particularly, flare forecasting algorithms, based on the detection of magnetic active regions (ARs) and associated flare probability estimation, are currently under development. The possible matching of MOTH II data with SDO/HMI and SDO/AIA images into a flux rope model, developed in collaboration between Harvard-Smithsonian CfA and MIT Laboratory for Nuclear Science, is being tested.

Vitamin D binding protein and vitamin D in human allergen-induced endobronchial inflammation.

Allergic asthma is a chronic disease of the airways associated with airway hyperresponsiveness, a variable degree of airflow obstruction, airway remodelling and a characteristic airway inflammation. Factors of the vitamin D axis, which include vitamin D metabolites and vitamin D binding protein (VDBP), have been linked to asthma, but only few data exist about their regulation in the lung during acute allergen-induced airway inflammation. Therefore, we analysed the regulation of factors of the vitamin D axis during the early- and late-phase reaction of allergic asthma. Fifteen patients with mild allergic asthma underwent segmental allergen challenge. VDBP was analysed in bronchoalveolar lavage fluid (BALF) and serum using the enzyme-linked immunosorbent assay (ELISA) technique. 25-hydroxyvitamin D(3)[25(OH)D(3)] and 1,25-dihydroxyvitamin D(3)[1,25(OH)(2)D(3)] were analysed by a commercial laboratory using the liquid chromatography-mass spectrometry (LC/MS) technique. VDBP (median 2·3, range 0·2-7·1 μg/ml), 25(OH)D(3) (median 0·060, range < 0·002-3·210 ng/ml) and 1,25(OH)(2)D(3) (median < 0·1, range < 0·1-2·8 pg/ml) were significantly elevated in BALF 24 h but not 10 min after allergen challenge. After correction for plasma leakage using the plasma marker protein albumin, VDBP and 25(OH)D(3) were still increased significantly while 1,25(OH)(2)D(3) was not. VDBP and 25(OH)D(3) were correlated with each other and with the inflammatory response 24 h after allergen challenge. Serum concentrations of all three factors were not influenced by allergen challenge. In conclusion, we report a significant increase in VDBP and 25(OH)D(3) in human BALF 24 h after allergen challenge, suggesting a role for these factors in the asthmatic late-phase reaction.

398 Seven Ventilators Delivering Nasal CPAP Challenged with Leakage: an Experimental Pilot Study

IntroductionNasal Continuous Positive Airway Pressure (nCPAP) is an established treatment for respiratory distress in neonates. Most modern ventilators are able to provide nCPAP. Compared to traditional nCPAP delivery systems ventilators...

Effects on geodetic VLBI measurements due to polarization leakage in S/X receivers

Geodetic very long baseline interferometry (VLBI) delivers time series of station positions and Earth orientation parameters. These series offer a viable and precise way to study Earth crustal and core dynamics and to support space navigation. Their accuracy is degraded by instrumental errors, of which polarization leakage is considered to be one of the largest that is not yet being addressed. Its effect on the data can be corrected, provided one knows the leakage characteristics of the receivers. For this purpose, we designed a VLBI session to measure the polarization leakage at 15 geodetic and very long baseline array stations over the frequency range from 8,212.99 to 8,932.99 MHz. We describe the polarization leakage measurements and the algorithm that was implemented to correct for its effect on the geodetic delay observables. Subsequently, we applied the correction for polarization leakage to the same data that were used to determine the leakage and checked for the resulting improvement. From the measured leakage terms, one would expect polarization leakage to affect the group delay measurements in 90% of the cases by 1.6 ps or less. This proved to be below the statistical noise in our single VLBI session, and hence, an improvement from the correction could not be detected. Applying this analysis in the context of VLBI2010, we provide a specification for the allowable polarization leakage to achieve the target submillimetre accuracy.

'Neo-Suterian' pump-turbine characteristics and their benefits

Conventional representations of the various operation modes of a pump-turbine (4-quadrant characteristics) have important disadvantages. While curves of Q11 vs n11 have singularities at E=0 and multiple values in the 'unstable' ranges, the curves EnD(QnD) get singular at n=0. As a remedy, one may split the characteristics into separate parts, and switch between them. Another approach introduced by P. Suter (1966, [1]) defines a different set of variables which avoids singularity and always remains unique-valued. Suter described this artifice for non-regulated pumps; but using it for regulated machines without modifications is not practical due to large distortions at small guide vane opening. A decisive improvement has been described by C.S. Martin [4]. It avoids the distortion of the head-vs-flow curves at low load. The present paper describes how further improvement is possible, in particular with regard to the representation of torque. A modified torque parameter is obtained by subtracting the shutoff torque; this parameter can be handled in the same practical way as the discharge. Other improvements concern the correction for leakage at small guide vane opening, and the treatment of very small and zero opening. These details are concerned with the problem of closed gate where Suter's concept does not work. Applications are demonstrated, not only how to represent the hydraulic performance (head vs. discharge and torque vs. discharge), but also for other characteristics, such as the development of pressure and pressure pulsation in various locations, or the steady-state and unsteady guide vane torque. The advantage of a set of continuous, single-valued functions for all those physical properties greatly simplifies computation of their behavior during transients. Moreover, the, Suterized' properties of pump-turbines of different specific speed are less different from each other than the conventional ones, a fact that facilitates application of available test data for later projects.

Glioblastoma: A Method for Predicting Response to Antiangiogenic Chemotherapy by Using MR Perfusion Imaging—Pilot Study

To derive a magnetic resonance (MR)-based imaging metric that reflects local perfusion changes resulting from the administration of angiogenic-inhibiting chemotherapy in patients with recurrent glioblastoma multiforme (GBM). In this retrospective Institutional Review Board-approved HIPAA-compliant study, 16 patients (12 men, four women; mean age, 51.8 years + or - 15.1 [standard deviation]) with recurrent GBM received bevacizumab every 3 weeks (15 mg per kilogram of body weight) as part of a clinical trial. Baseline MR images were acquired, and follow-up images were acquired every 6 weeks thereafter until tumor progression or death. Imaging included perfusion and T1-weighted contrast material-enhanced MR imaging. Perfusion images were analyzed both with and without correction for contrast material leakage. The volumes of interest were selected as enhancing voxels on T1-weighted contrast-enhanced MR images. Relative cerebral blood volume (rCBV) maps were created from analysis of MR perfusion images. The volumes of interest were used to calculate the following parameters: size, mean rCBV, mean leakage coefficient K(2), and hyperperfusion volume (HPV), which is the fraction of the tumor with an rCBV higher than a predetermined threshold. Percent change in each parameter from baseline to first follow-up was compared with time to progression (TTP) by using a Cox proportional hazards model with calculation of hazard ratios. The most significant hazard ratio was seen with a DeltaHPV cutoff of rCBV greater than 1.00 (hazard ratio, 1.077; 95% confidence interval: 1.026, 1.130; P = .002). The only significant ratios greater than one were those that resulted from perfusion calculated as mean rCBV and DeltaHPV. The ratios were also higher after correction for leakage. This pilot study derived an imaging metric (HPV) that reflects local perfusion changes in GBMs. This metric was found to show a significantly improved correlation to TTP as compared with more commonly used metrics.

Diffuse optical tomographic imager using a single light source

Near-infrared diffuse optical tomography (DOT) technique has the capability of providing good quantitative reconstruction of tissue absorption and scattering properties with additional inputs such as input and output modulation depths and correction for the photon leakage. We have calculated the two-dimensional (2D) input modulation depth from three-dimensional (3D) diffusion to model the 2D diffusion of photons. The photon leakage when light traverses from phantom to the fiber tip is estimated using a solid angle model. The experiments are carried for single (5 and 6 mm) as well as multiple inhomogeneities (6 and 8 mm) with higher absorption coefficient in a homogeneous phantom. Diffusion equation for photon transport is solved using finite element method and Jacobian is modeled for reconstructing the optical parameters. We study the development and performance of DOT system using modulated single light source and multiple detectors. The dual source methods are reported to have better reconstruction capabilities to resolve and localize single as well as multiple inhomogeneities because of its superior noise rejection capability. However, an experimental setup with dual sources is much more difficult to implement because of adjustment of two out of phase identical light probes symmetrically on either side of the detector during scanning time. Our work shows that with a relatively simpler system with a single source, the results are better in terms of resolution and localization. The experiments are carried out with 5 and 6 mm inhomogeneities separately and 6 and 8 mm inhomogeneities both together with absorption coefficient almost three times as that of the background. The results show that our experimental single source system with additional inputs such as 2D input/output modulation depth and air fiber interface correction is capable of detecting 5 and 6 mm inhomogeneities separately and can identify the size difference of multiple inhomogeneities such as 6 and 8 mm. The localization error is zero. The recovered absorption coefficient is 93% of inhomogeneity that we have embedded in experimental phantom.

The residual protonmotive force in mitochondria after an oxygen pulse.

Both from irreversible thermodynamics and from mass-action kinetics it can be derived that upon anaerobiosis in an oxygen-pulse experiment the protonmotive force across a mitochondrial membrane undergoes a sudden drop. Under representative conditions the protonmotive force after the drop (the residual protonmotive force) is shown to be less than 3 kJ . mol-1 as opposed to steady-state values for the protonmotive force of 19 kJ . mol-1. It is concluded that correction for proton leakage in pulse experiments by back extrapolation underestimate proton leakage. Consequently the observed H+/O stoichiometries must underestimate the true H+/O ratios.

Inversion MOS capacitance extraction for high-leakage dielectrics using a transmission line equivalent circuit

Accurate measurement of MOS transistor inversion capacitance with a physical silicon dioxide thickness less than 20 /spl Aring/ requires correction for the direct tunneling leakage. This work presents a capacitance model and extraction based on the application of a lossy transmission line model to the MOS transistor. This approach properly accounts for the leakage current distribution along the channel and produces a gate length dependent correction factor for the measured capacitance that overcomes discrepancies produced through use of previously reported discrete element based models. An extraction technique is presented to determine the oxide's tunneling and channel resistance of the transmission line equivalent circuit. This model is confirmed by producing consistent C/sub 0x/ measurements for several different gate lengths with physical silicon dioxide thickness of 9, 12, and 18 /spl Aring/.

Preservation and incubation time-induced bias in tracer-aided grazing studies on meiofauna

A recent review suggests that meiofauna are important grazers of microphytobenthic primary production as well as of bacterial secondary production. The potential importance of meiofauna grazers may nevertheless have systematically been underestimated, since label leakage from chemically preserved animals has hitherto not been accounted for. Furthermore, a majority of studies have used relatively long incubation times and assumed, rather than proved, that label recycling over this period is negligible. In the present study we tested the influence of sample preservation on label retention in the marine nematode Pellioditis marina Andrassy, 1983 fed 3H-labelled bacteria. Label loss from formaldehyde-preserved specimens averaged 40% after 1 h preservation and amounted to a maximum of 85% after 24 h in formaldehyde, irrespective of formaldehyde concentration; no further leakage occurred beyond 24 h. Glutaraldehyde and ethanol yielded significantly better and poorer results, respectively, but the former fixative still yielded label losses of up to 70%. A comparison of label uptake as a function of time with observations on ingestion and defecation behaviour suggest that on time scales of hours an indication of assimilation (after correction for label leakage) rather than of ingestion is obtained. When killed with formaldehyde at room temperature, P. marina egested a significant part of its gut contents. The sources of bias identified here may have generally led to significant underestimations of true grazing rates. The cumulative effect of label leakage, prey egestion and long incubation times, each at the highest rates observed in this study, may yield as much as a 15-fold underestimation of true food consumption. Cooling samples on ice and fixation with ice-cold formaldehyde, followed by immediate freeze-preservation, and sorting of the nematodes within 2 h after thawing, gives average values for label leakage of 50%, and hence allows the application of a proximate correction factor for label losses of 2.

Tracing the Efficiency of Secondary Treatment Systems

A technique for mapping the three-dimensional performance of secondary treatment systems and for studying the behavior of specific compounds in-situ is described. [14C]Oleic acid was added to samples collected from various locations in the system. Each mixture was placed in a vial capped at both ends with semipermeable membranes, returned to its original position in the lagoon, and then retrieved after 1 day. The amount of radioactivity remaining, after cor rection for leakage and nonbiological losses, is a measure of biological activity. The approach revealed that water-column biodegradation was only one of many pathways for oleic acid removal, with sorption to solids also being important and, perhaps, dominant. Furthermore, it rationalized performance differences between an AST (activated sludge treatment) system and an ASB (aerated stabilization basin).

EFFECT OF INTRATRACHEAL INSTALLATION OF SURFACTANT OH LUNG FUNCTION AND FUNCTIONAL RESIDUAL CAPACITY (FRC) IN PREMATURE INFANTS WITH RESPIRATORY DISTRESS SYNDROME (RDS)

To understand the mechanism behind improved oxygenation after surfactant in infants with RDS we analysed changes in lung compliance (CL, ml/cmH2O), lung resistance (RL, cmH2O/l/s/cm), overdistention (C20/C1), FRC (ml) and oxygen need (FiO2). Data were collected serially in nine infants (CurosurfR two, ExosurfR seven) (BW: 1389 ± 540 g) prior to and post surfactant treatment. Lung mechanics were determined by a differential pressure transducer and pneumotachography (PEDSR). FRC was measured by a helium dilution technique (PANDAR) with correction for gas leakage. Ventilator settings (except FiO2) were if possible kept constant during the study. (Data given as mean±SEM).Surfactant significantly increases FRC, while lung compliance and resistance (during mechanical breath) do not improve. The improved oxygenation after surfactant treatment is probably related to increased lung volume.

The contribution of the ‘pacemaker’ current (if) to generation of spontaneous activity in rabbit sino‐atrial node myocytes.

1. The contribution to the diastolic depolarization of the hyperpolarization-activated current, if, relative to other components was investigated in isolated rabbit sino-atrial (SA) node myocytes. 2. During the diastolic phase the membrane potential depolarized by 0.1096 +/- 0.014 V/s, which requires only about 3 pA of inward current in a cell with an average capacity of 30 pF. The problem of which ionic component is responsible for initiating the diastolic depolarization was investigated by analysing the composition and the properties of the net inward current in the diastolic range of voltages. 3. The measured instantaneous 'background' current activated during voltage clamp steps from a holding potential of -35 mV was outward positive to approximately -61 mV, and had a region of negative slope conductance from -45 to -35 mV. 4. The instantaneous component lost its rectifying behaviour in the presence of Ni2+ (100 microM) and nitrendipine (10 microM). These blockers of Ca(2+)-dependent currents modified the instantaneous I-V relation at voltages positive to -45 to -50 mV, thus implying that Ca2+ currents become important at less negative potentials than -50 mV, towards the very end of diastolic depolarization. 5. Possible errors introduced by voltage clamp analysis with the whole-cell method on the instantaneous current and on if measurement were evaluated. Leakage through the seal resistance caused the instantaneous I-V relation to be displaced in the inward direction at negative voltages. Correction for the seal leakage moved the reversal potential for the instantaneous current toward the negative direction from -61 to approximately -66 mV. Thus, no depolarization can be driven by the background current beyond -66 mV. 6. During voltage clamp analysis, lack of series-resistance compensation led to lack of intracellular voltage control, as was apparent using a second pipette on the same cell. This slowed activation of if and led to a 1.5- to 2-fold reduction of if size in the range -55 to -115 mV. Thus, uncorrected measurements of the instantaneous component and of if may concur to underestimate the role of if in pacemaking. 7. These results lead to the conclusion that in the SA node cells analysed, pacemaker activity is generated with the essential contribution of the hyperpolarization-activated current, if. Numerical computation of SA node cell activity using an extension of the DiFrancesco-Noble model shows that the if-activation hypothesis can account for the presence of spontaneous action potentials and their sensitivity to if changes.