Accurate Ratio Measurements Research Articles

A Numerical Analysis of the Effects of Equivalence Ratio Measurement Accuracy on the Engine Efficiency and Emissions at Varied Compression Ratios

Increasingly stringent regulations to reduce vehicle emissions have made it important to study emission mitigation strategies. Highly accurate control of the air-fuel ratio is an effective way to reduce emissions. However, a less accurate sensor can lead to reduced engine stability and greater variability in engine efficiency and emissions. Additionally, internal combustion engines (ICE) are moving toward higher compression ratios to achieve higher thermal efficiency and alleviate the energy crisis. The objective of this investigation was to analyze the significance of the accuracy of air-fuel ratio measurements at different compression ratios. In this study, a calibrated 1D CFD model was used to analyze the performance and emissions at different compression ratios. The results showed that carbon monoxide (CO) and nitrogen oxides (NOx) were sensitive to the equivalence ratio regardless of the compression ratio. With a slight change in the equivalence ratio, a high compression ratio had little effect on the change in engine performance and emissions. Moreover, with the same air-fuel ratio, an excessively high compression ratio (CR = 12) might result in knocking phenomenon, which increases the fluctuation of the engine output parameters and reduces engine stability. Overall, for precise control of combustion and thermal efficiency improvement, it is recommended that the measurement accuracy of the equivalence ratio is higher than 1% and the recommended value of the compression ratio are roughly 11.

Actinide ions for testing the spatial α -variation hypothesis

Testing the spatial variation of fine-structure constant $\alpha$ indicated in [Webb et al., Phys. Rev. Lett. 107, 191101 (2011)] with terrestrial laboratory atomic measurements requires at least $\dot{\alpha}/\alpha \sim 10^{-19}~\textrm{y}^{-1}$ sensitivity. We conduct a systematic search of atomic systems for such a test that have all features of the best optical clock transitions leading to possibility of the frequency measurements with fractional accuracy on the level of $10^{-18}$ or better and have a factor of 100 extra enhancement of $\alpha$-variation in comparisons to experimental frequency ratio measurement accuracy. We identify the pair of actinide Cf$^{15+}$ and Es$^{16+}$ ions as the best system for a test of spatial $\alpha-$variation hypothesis as it satisfies both of these requirements and have sufficiently simple electronic structure to allow for high-precision predictions of all atomic properties required for rapid experimental progress.

Measurement of capacitance and resistance using two perfectly synchronized voltage sources

A programmable bridge has been constructed by using two arbitrary waveform generators and DVM as a null-detector for capacitance and resistance measurements. The generators are controlled by a software program which has been specially designed to achieve their optimum performance. Methodology of this bridge has been introduced demonstrating the best way to get accurate ratio measurements up to the accuracy level of 10−5. Our bridge has been used, through this research, to get resistance to resistance and capacitance to resistance ratios at different frequencies. Validation of this bridge has been carried out through comparisons with another conventional bridge, which show satisfying agreement. In addition, the bridge has been verified by calculating its asymmetry which is about 0.65ppm in some cases. Finally, the uncertainty budget for the bridge measurements has been introduced in details.

High-Current CT Calibration Using a Sampling Current Ratio Bridge

A measurement setup is developed for the accurate ratio measurement of ac current transformers (CTs) for primary currents up to 5 kA. A unique property of the system is the use of high-quality digitizers for sampling of the secondary current signals and step-down transformers with different current ratios. This allows for accurate comparison of CTs even when their nominal ratios are not equal. The calibration results of the key components in the setup show that the sampling current ratio bridge has a ratio uncertainty of better than 2 $\mu{\rm A/A}$ in magnitude and 0.8 $\mu{\rm rad}$ in phase for CT-under-test current ratios that do not differ by more than a factor of 5 from one of the ratios in the reference CT. The linearity of the bridge for input currents changing between 1% and 120% of nominal input current is better than 4 $\mu{\rm A/A}$ in magnitude and 0.5 $\mu{\rm rad}$ in phase.

Method of standard additions for arsenic measurements in water by ICP sector field mass spectrometry at accuracy comparable to isotope dilution

Mathematical model of the method of additions was reviewed to exclude the dilution and mass irreproducibility effects and assure the linear calibration. Selenium was identified as a high quality internal standard for arsenic measurements. At increased ratio measurement accuracy instrumental effects are important, and capabilities of the instrument must be carefully tested and accounted for. In measurements with double focusing electric and magnetic fields mass spectrometer Element 2 at medium mass resolution need for full integration of the peaks and role of the low frequency noise was evident. Averaging of the final results provided better accuracy of determination in comparison to the mean values of the intermediate data. If suitable internal standards can be selected, the method of standard additions is found to provide measurement accuracy comparable to that of isotope dilution. Comparison of the analytical signal of the test sample from direct measurements and the calibration graph is recommended as a test of the level of compensation for the possible matrix effects.

Constraints on cosmic-ray positron excess and average pulsar parameters

Recent, accurate ratio measurements in cosmic rays allow us to distinguish among different estimates of secondary positron production in the interstellar medium (ISM), provided the effect of solar modulation and solar polarity are properly taken into account. Data above a few GeV indicate that a possible extra component of positrons could be required in addition to the secondaries. This positron excess is compatible with the hypothesis of pair production at the polar cap of mature pulsars. Assuming only pulsar contributions without any exotic contributions such as dark-matter annihilation, the average parameters of Galactic pulsars contributing to positron and electron interstellar fluxes were obtained. These parameter values are found near the peak of the distributions of the observed characteristics of radio pulsars. The studied gamma-ray pulsar sample is too small to make any conclusion. The expected ratio from the PAMELA experiment currently in orbit is reported in this paper. The GLAST mission will allow us to double-check our findings about the role of pair production at the pulsar polar cap and outer gap.

A Vector Network Analyzer Based on Seven-Port Wave-Correlator

A seven-port wave-correlator based vector network analyzer is proposed. The seven-port wave-correlator is a combination of two six-port wave-correlators which share common components. Furthermore, the complex wave ratio measurement accuracy is improved since the input signals can be directly detected by the side-arm ports. A seven-port wave-correlator is fabricated using microstrip branch line couplers. The performance of the wave-correlator and the constructed network analyzer are evaluated, and the measurement accuracy is confirmed.

Temperature Measurements in the Solar Transition Region Using NiiiLine Intensity Ratios

UV emission from B-like N and O ions a rather rare opportunity for recording spectral lines in a narrow wavelength range that can potentially be used to derive temperatures relevant to the solar transition region. In these ions, the line intensity ratios of the type (2s2p(sup 2) - 2p(sup 3)) / (2s(sup 2)2p - 2s2p(sup 2)) are very sensitive to the electron temperature. Additionally, the lines involving the ratios fall within a range of only - 12 A; in N III the lines fall in the 980 - 992 A range and in O IV in the 780 - 791 A range. In this work, we explore the use of these atomic systems, primarily in N III, for temperature diagnostics of the transition region by analyzing UV spectra obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer flown on the Solar and Heliospheric Observatory (SOHO). The N III temperature-sensitive line ratios are measured in more than 60 observations. Most of the measured ratios correspond to temperatures in the range 5.7x10(exp 4) - 6.7x10(exp 4) K. This range is considerably lower than the calculated temperature of maximum abundance of N III, which is approx. 7.6x10(exp 4) K. Detailed analysis of the spectra further indicates that the measured ratios are probably somewhat overestimated due to resonant scattering effects in the 2s(sup 2)2p - 2s2p(sup 2) lines and small blends in the 2s2p(sup 2) - 2p3 lines. Actual lower ratios would only increase the disagreement between the ionization balance calculations and present temperature measurements based on a collisional excitation model. In the case of the O IV spectra, we determined that due to the close proximity in wavelength of the weak line (2s2p(sup 2)-2p3 transitions) to a strong Ne VIII line, sufficiently accurate ratio measurements cannot be obtained. Subject headings: atomic data --- atomic processes --- Sun: transition region --- Sun: U V radiation --- techniques: spectroscopic

Design considerations for a future injection system for radocarbon AMS measurements

In planning for a possible upgrade to the Oxford AMS system (dedicated to C-14 measurements), we have given thought to novel as well as conventional designs of injection which achieve both a high level of accuracy and also permit C-14 detection with negligible background due to misidentification. Experiments at Oxford in which sputtered beams from graphite are directly injected (no mass separation) give limits on the sufficient mass resolution to achieve unambiguous C-14 detection. These will be discussed. Our experience with the CO 2 source indicates that space charge effects can become the dominant problem in achieving isotope ratio measurement accuracy and we believe should be taken into account in the design of high beam current systems. We will outline possible designs for a new system with these effects in mind. In particular, we hope to present a feasibility study for a pulsed magnet design.

Calibrator for alternating voltage, current, and power

A computer-controlled calibrator capable of delivering AC sinusoidal and distorted waveform voltage, current, and power with an accuracy of several parts per million is described. The reference AC voltage is obtained using digital-to-analog conversion and the reference AC current by applying the reference voltage to a reference AC resistor. The phase relation is obtained digitally. A combination of feedback and error-feedforward control strategy, together with the current comparator technique for very accurate ratio measurements, is applied. The parts per million stability of the calibrator permits the use of a multiplexing program for varying the settings and for monitoring several instruments over a long period of time.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Reply [to “Comments on paper by S. E. Poet, H. E. Moore, and E. A. Martell, ‘Lead 210, bismuth 210, and polonium 210 in the atmosphere: Accurate ratio measurement and application to aerosol residence time determination’”

Reply [to “Comments on paper by S. E. Poet, H. E. Moore, and E. A. Martell, ‘Lead 210, bismuth 210, and polonium 210 in the atmosphere: Accurate ratio measurement and application to aerosol residence time determination’”

Comment on paper by S. E. Poet, H. E. Moore, and E. A. Martell, ‘Lead 210, bismuth 210, and polonium 210 in the atmosphere: Accurate ratio measurement and application to aerosol residence time determination’

Comment on paper by S. E. Poet, H. E. Moore, and E. A. Martell, ‘Lead 210, bismuth 210, and polonium 210 in the atmosphere: Accurate ratio measurement and application to aerosol residence time determination’

Comments on paper by S. E. Poet, H. E. Moore, and E. A. Martell, ‘Lead 210, bismuth 210, and polonium 210 in the atmosphere: Accurate ratio measurement and application to aerosol residence time determination’

Comments on paper by S. E. Poet, H. E. Moore, and E. A. Martell, ‘Lead 210, bismuth 210, and polonium 210 in the atmosphere: Accurate ratio measurement and application to aerosol residence time determination’

Reply [to “Comment on paper by S. E. Poet, H. E. Moore, and E. A. Martell, ‘Lead 210, bismuth 210, and polonium 210 in the atmosphere: Accurate ratio measurement and application to aerosol residence time determination’”

Reply [to “Comment on paper by S. E. Poet, H. E. Moore, and E. A. Martell, ‘Lead 210, bismuth 210, and polonium 210 in the atmosphere: Accurate ratio measurement and application to aerosol residence time determination’”

Lead 210, bismuth 210, and polonium 210 in the atmosphere: Accurate ratio measurement and application to aerosol residence time determination

Procedures developed for the sequential chemical separation and radiochemical analysis of 210Pb, 210Bi, 210Po, and 90Sr are described. Results from the measurements of these radioisotopes in surface air and precipitation are presented and discussed in relation to their sources and their application as tracers for the estimation of the residence times of particles in the lower atmosphere. It is concluded that the simple steady-state model does not apply to these long-lived radon daughters and that published residence time estimates based on 210Po/210Pb ratios are incorrect and too long. On the basis of 210Bi/210Pb activity ratios, correcting for the presence of an assumed secular equilibrium component of 210Pb, 210Bi, and 210Po, we estimate a mean atmospheric residence time of about 4 days for particles in the lower troposphere and about 1 week for particles in precipitation. Further tests of the steady-state assumption and other factors affecting such estimates are in progress.