scholarly journals Impact of sampling frequency in the analysis of tropospheric ozone observations

2012 ◽  
Vol 12 (15) ◽  
pp. 6757-6773 ◽  
Author(s):  
M. Saunois ◽  
L. Emmons ◽  
J.-F. Lamarque ◽  
S. Tilmes ◽  
C. Wespes ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Tropospheric Ozone ◽  
High Frequency ◽  
Low Frequency ◽  
Sampling Frequency ◽  
Vertical Profiles ◽  
Sampling Uncertainty ◽  
Frequency Sampling ◽  
Typical Frequency

Abstract. Measurements of ozone vertical profiles are valuable for the evaluation of atmospheric chemistry models and contribute to the understanding of the processes controlling the distribution of tropospheric ozone. The longest record of ozone vertical profiles is provided by ozone sondes, which have a typical frequency of 4 to 12 profiles a month. Here we quantify the uncertainty introduced by low frequency sampling in the determination of means and trends. To do this, the high frequency MOZAIC (Measurements of OZone, water vapor, carbon monoxide and nitrogen oxides by in-service AIrbus airCraft) profiles over airports, such as Frankfurt, have been subsampled at two typical ozone sonde frequencies of 4 and 12 profiles per month. We found the lowest sampling uncertainty on seasonal means at 700 hPa over Frankfurt, with around 5% for a frequency of 12 profiles per month and 10% for a 4 profile-a-month frequency. However the uncertainty can reach up to 15 and 29% at the lowest altitude levels. As a consequence, the sampling uncertainty at the lowest frequency could be higher than the typical 10% accuracy of the ozone sondes and should be carefully considered for observation comparison and model evaluation. We found that the 95% confidence limit on the seasonal mean derived from the subsample created is similar to the sampling uncertainty and suggest to use it as an estimate of the sampling uncertainty. Similar results are found at six other Northern Hemisphere sites. We show that the sampling substantially impacts on the inter-annual variability and the trend derived over the period 1998–2008 both in magnitude and in sign throughout the troposphere. Also, a tropical case is discussed using the MOZAIC profiles taken over Windhoek, Namibia between 2005 and 2008. For this site, we found that the sampling uncertainty in the free troposphere is around 8 and 12% at 12 and 4 profiles a month respectively.

scholarly journals Impact of sampling frequency in the analysis of tropospheric ozone observations

2011 ◽  
Vol 11 (10) ◽  
pp. 27107-27137
Author(s):  
M. Saunois ◽  
L. Emmons ◽  
J.-F. Lamarque ◽  
S. Tilmes ◽  
C. Wespes ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Tropospheric Ozone ◽  
Sampling Error ◽  
Data Sets ◽  
Vertical Profiles ◽  
Sampling Uncertainty ◽  
Data Set ◽  
Northern Hemispheric ◽  
The One ◽  
Typical Frequency

Abstract. The measurements of the ozone vertical profiles are valuable for the evaluation of atmospheric chemistry models and contribute to the understanding of the processes controlling the distribution of tropospheric ozone. The longest record of the ozone vertical profiles is provided by ozone sondes, which have a low time resolution with a typical frequency of 12 or 4 profiles a month. Here we discuss and quantify the uncertainty in the analysis of such data sets using high frequency MOZAIC (Measurements of OZone, water vapor, carbon monoxide and nitrogen oxides by in-service AIrbus airCraft) profiles data sets, such as the one over Frankfurt. We subsampled the MOZAIC data set at the two typical ozone sonde frequencies. We find that the uncertainty introduced by the coarser sampling is around 8% for a 12 profiles a month frequency (14% for a 4 profiles a month frequency) in the free troposphere over Frankfurt. As a consequence, this uncertainty at the lowest frequency is higher than the typical 10% accuracy of the ozone sondes and should be carefully considered for observation comparison and model evaluation. We found that the average intra-seasonal variability represented in the samples is similar to the sampling uncertainty and could also be used as an estimate of the sampling error in some Northern Hemisphere cases. The sampling impacts substantially the inter annual variability and the trend derived over the period 1995–2008 both in magnitude and in sign throughout the troposphere. Therefore, the sampling effect could be part of the observed discrepancies between European sites. Similar results regarding the sampling uncertainty are found at five other Northern Hemispheric sites. Also, a tropical case is discussed using the MOZAIC profiles taken over Windhoek, Namibia between 2005 and 2008.

scholarly journals Low-Frequency Signal Sampling Method Implemented in a PLC Controller Dedicated to Applications in the Monitoring of Selected Electrical Devices

Electronics ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 442
Author(s):  
Marcin Jaraczewski ◽  
Ryszard Mielnik ◽  
Tomasz Gębarowski ◽  
Maciej Sułowicz
Keyword(s):  
Power System ◽  
Reactive Power ◽  
Low Frequency ◽  
Sampling Frequency ◽  
Electrical Signal ◽  
Distortion Factor ◽  
Electrical Devices ◽  
Frequency Sampling ◽  
Sampled Signal ◽  
Band Limited

High requirements for power systems, and hence for electrical devices used in industrial processes, make it necessary to ensure adequate power quality. The main parameters of the power system include the rms-values of the current, voltage, and active and reactive power consumed by the loads. In previous articles, the authors investigated the use of low-frequency sampling to measure these parameters of the power system, showing that the method can be easily implemented in simple microcontrollers and PLCs. This article discusses the methods of measuring electrical quantities by devices with low computational efficiency and low sampling frequency up to 1 kHz. It is not obvious that the signal of 50–500 Hz can be processed using the sampling frequency of fs = 47.619 Hz because it defies the Nyquist–Shannon sampling theorem. This theorem states that a reconstruction of a sampled signal is only guaranteed possible for a bandlimit fmax < fs, where fmax is the maximum frequency of a sampled signal. Therefore, theoretically, neither 50 nor 500 Hz can be identified by such a low-frequency sampling. Although, it turns out that if we have a longer period of a stable multi-harmonic signal, which is band-limited (from the bottom and top), it allows us to map this band to the lower frequencies, thus it is possible to use the lower sampling ratio and still get enough precise information of its harmonics and rms value. The use of aliasing for measurement purposes is not often used because it is considered a harmful phenomenon. In our work, it has been used for measurement purposes with good results. The main advantage of this new method is that it achieves a balance between PLC processing power (which is moderate or low) and accuracy in calculating the most important electrical signal indicators such as power, RMS value and sinusoidal-signal distortion factor (e.g., THD). It can be achieved despite an aliasing effect that causes different frequencies to become indistinguishable. The result of the research is a proposal of error reduction in the low-frequency measurement method implemented on compact PLCs. Laboratory tests carried out on a Mitsubishi FX5 compact PLC controller confirmed the correctness of the proposed method of reducing the measurement error.

Magnetic Permeability and Relaxation Frequency in High Frequency Magnetic Materials.

2001 ◽  
Vol 674 ◽  
Author(s):  
M.I. Rosales ◽  
H. Montiel ◽  
R. Valenzuela
Keyword(s):  
High Frequency ◽  
Domain Walls ◽  
Magnetocrystalline Anisotropy ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Anisotropy Constant ◽  
Relaxation Frequency ◽  
Resonance Relaxation ◽  
Frequency Behavior

ABSTRACTAn investigation of the frequency behavior of polycrystalline ferrites is presented. It is shown that the low frequency dispersion (f < 10 MHz) of permeability is associated with the bulging of pinned domain walls, and has a mixed resonance-relaxation character, closer to the latter. It is also shown that there is a linear relationship between the magnetocrystalline anisotropy constant, K1, and the relaxation frequency. The slope of this correlation depends on the grain size. Such a relationship could allow the determination of this basic parameter from polycrystalline samples.

Required Data Collection Times for Steady and Quasi-steady Experiments

2017 ◽  
Author(s):  
Robert F. Roddy ◽  
David E. Hess
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Frequency Noise ◽  
Surface Ship ◽  
System A ◽  
Low Pass ◽  
Collection Period ◽  
Almost All ◽  
Low Pass Filters

One of the requirements in performing steady or quasi-steady experiments is the determination of adequate collection times so that the data will not be biased due to low frequency energy in the data stream. Since virtually all steady experiments run at DTMB have low pass filters in line with the signal conditioning, high frequency noise is not a consideration in determining the required collection times. At both EMB and DTMB almost all of the surface ship drag measurements were made using gravity type balances until about 1970. These balances used both springs and dampers to modify the natural frequency of the system so that a good average model drag could be determined in a 5-6 sec collection period. Submarine model experiments began using block gages to measure drag beginning in the late 1950's. For these experiments crude methods were used to damp the output data but, to the author’s knowledge, no methods were ever put into place that was analogous to the springs and damper system. A method for determining the required collection times for any steady or quasi-steady experiment is presented along with sample cases showing the necessity for, and the utility of, using such a method.

Effects of Off-Frequency Detection in Brief-Tone Audiometry

1974 ◽  
Vol 17 (4) ◽  
pp. 576-588 ◽  
Author(s):  
Michele Spence ◽  
Lawrence L. Feth
Keyword(s):  
High Frequency ◽  
Temporal Integration ◽  
Low Frequency ◽  
High Frequency Hearing Loss ◽  
Frequency Detection ◽  
Stimulus Artifact ◽  
Brief Tones ◽  
High Pass

Many studies of auditory temporal integration by pathological ears have used listeners with an abrupt high-frequency hearing loss. While this configuration may lend itself to use of the listener as his own control, it presents the opportunity for detection of the low-frequency energy of the brief-tone bursts. This study was designed to assess the role of low-frequency energy in the determination of brief-tone thresholds of listeners with such abrupt high-frequency losses. Low-frequency energy was reduced to subthreshold levels by passing the brief tones through a filter system which had a sharp high-pass characteristic. For both normal and impaired listeners, no significant differences in threshold were found between filtered and unfiltered brief tones. Thus, we must conclude that although the opportunity for off-frequency detection is present, the abnormal temporal integration functions cannot be attributed to stimulus artifact.

The Twin Clinical Method in Dermatology

1970 ◽  
Vol 19 (1-2) ◽  
pp. 257-257
Author(s):  
R. Cavalieri
Keyword(s):  
Epidermolysis Bullosa ◽  
High Frequency ◽  
Skin Diseases ◽  
Acne Vulgaris ◽  
Low Frequency ◽  
Clinical Method ◽  
Clinical Evolution ◽  
High Concordance ◽  
Mz Twins

Genetic skin diseases have been considered with respect to their population and family frequencies, as well as to their concordance values, in MZ and DZ twin pairs. The clinical evolution of the disease has been further considered in its various stages and compared in MZ and DZ twins, concordant for the disease.The material consisted of 100 twin pairs, with at least one member affected, subdivided with respect to concordance and zygosity. For each dermatosis, then, the population and family frequencies have been calculated. The following dermatoses could be studied: psoriasis, acne vulgaris, keratosis pilaris, alopecia areata, epidermolysis bullosa and dermatitis seborrheica.A high concordance of clinical evolution in MZ twins has appeared to correspond to a low frequency of the disease, while a high frequency appears to correspond to low concordance values. This finding may be very useful for a better understanding of the disease's inheritance, as well as of its penetrance and expression.It has been finally possible to evaluate the hereditary quantum vs. the environmental one in the determination of a dermatosis, by means of Holzinger's coefficient of heredity (H). The estimates of the latter vary from 35 to 50% in the various dermatoses examined.

DETERMINATION OF THE INFLUENCE OF STRUCTURAL ELEMENTS ON ACOUSTIC EFFICIENCY AND BACK PRESSURE IN EXHAUST AND SUCTION NOISE SILENCERS

Akustika ◽  
2021 ◽  
pp. 210-216
Author(s):  
Nickolay Ivanov ◽  
Aleksandr Shashurin ◽  
Aleksandr Burakov
Keyword(s):  
Structural Design ◽  
High Frequency ◽  
Experimental Studies ◽  
Low Frequency ◽  
Back Pressure ◽  
Noise Generation ◽  
Structural Elements ◽  
The Relationship

The features of noise generation processes in exhaust and suction noise silencers are shown. A method for testing silencers has been developed. The classification of the main structural elements of exhaust and suction noise silencers, depending on the purpose, is proposed. Experimental studies of the relationship between the acoustic efficiency and the back pressure of silencers from the structural design of the elements are performed. The factors influencing the efficiency in the low-frequency and high-frequency regions of the spectrum are determined: the volume of silencers, the number of chambers, perforation, sound absorption, flow ejection, etc. Recommendations for the design of noise silencers are proposed.

scholarly journals Low Frequency Radio Astronomy from the Moon

1998 ◽  
Vol 11 (2) ◽  
pp. 988-989
Author(s):  
D.L. Jones ◽  
K.W. Weiler
Keyword(s):  
High Frequency ◽  
Angular Resolution ◽  
Low Frequency ◽  
High Angular Resolution ◽  
Radio Sources ◽  
The Moon ◽  
Interstellar Scintillation ◽  
Wide Range ◽  
Lunar Farside

AbstractThe radio sky at frequencies of several MHz and below is essentially unexplored with high angular resolution due to refraction and opacity in the Earth’s ionosphere. An interferometer array in space providing arcminute resolution images would allow a wide range of problems in solar, planetary, galactic, and extragalactic astronomy to be attacked. These include the evolution of solar and planetary radio bursts, interplanetary and interstellar scintillation, the distribution of low energy cosmic rays and diffuse ionized hydrogen in our galaxy, the determination of spectral turnover frequencies and magnetic field strengths in galactic and extragalactic radio sources, searches for “fossil” radio galaxies which are no longer detectable by high frequency surveys, and searches for new sources of coherent radio emission. In addition, it is likely that unexpected objects and emission processes will be discovered by such an instrument, as has often happened when high resolution observations first become possible in a new spectral region. The Moon can provide shielding from terrestrial interference (and from the Sun half of the time) and consequently the lunar farside surface offers an ideal site of a low frequency radio array.

scholarly journals Exact and limiting solutions of fluid flow for axially oscillating cylindrical pipe and annulus

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
U. K. Sarkar ◽  
Nirmalendu Biswas
Keyword(s):  
Velocity Distribution ◽  
High Frequency ◽  
Oscillatory Flow ◽  
Stokes Equations ◽  
Low Frequency ◽  
Navier Stokes ◽  
Cylindrical Pipe ◽  
Navier Stokes Equations ◽  
Cylindrical Annulus

AbstractThe Navier–Stokes equations have been solved to derive the expressions of the velocity distributions for two cases: (1) oscillatory flows inside and outside of an axially oscillating cylindrical pipe, and (2) oscillatory flow inside an axially oscillating cylindrical annulus. In both the cases, in addition to the exact expressions for the velocity profiles, particular emphasis has been given for the determination of approximate velocity distributions for the high frequency and low frequency or quasi-static limits. It is shown that, for sufficiently large value of an appropriate frequency parameter, the velocity distribution inside the axially or longitudinally oscillating cylindrical annulus can be approximated as a superposition of the velocity distribution inside an axially oscillating cylindrical pipe of radius $${\bar R_o}$$ R ¯ o and the velocity distribution outside an axially oscillating cylindrical pipe of radius $${\bar R_i}$$ R ¯ i , where $${\bar R_i}$$ R ¯ i and $${\bar R_o}$$ R ¯ o are the inner and outer radii of the axially oscillating annulus, respectively.

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