The Reduction of Bias Error in Transfer Function Estimates Using FFT-Based Analyzers

1984 ◽  
Vol 106 (1) ◽  
pp. 29-35 ◽  
Author(s):  
P. Cawley
Keyword(s):  
Transfer Function ◽  
Random Excitation ◽  
Analogue Computer ◽  
Bias Error ◽  
Testing Time ◽  
Theoretical Predictions ◽  
Set Up ◽  
Modal Mass ◽  
Time Required ◽  
Good Agreement

The susceptibility to bias error of two methods for computing transfer (frequency response) functions from spectra produced by FFT-based analyzers using random excitation has been investigated. Results from tests with an FFT analyzer on a single degree-of-freedom system set up on an analogue computer show good agreement with the theoretical predictions. It has been shown that, around resonance, the bias error in the transfer function estimate H2 (Syy/Sxy*) is considerably less than that in the more commonly used estimate, H1 (Sxy/Sxx). The record length, and hence the testing time, required for a given accuracy is reduced by over 50 percent if the H2 calculation procedure is used. The analysis has also shown that if shaker excitation is used on lightly damped structures with low modal mass, it is important to minimize the mass of the force gage and the moving element of the shaker.

The Accuracy of Frequency Response Function Measurements Using FFT-Based Analyzers With Transient Excitation

1986 ◽  
Vol 108 (1) ◽  
pp. 44-49 ◽  
Author(s):  
P. Cawley
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Frequency Response Function ◽  
Random Excitation ◽  
Frequency Resolution ◽  
Impact Excitation ◽  
Analogue Computer ◽  
Bias Error ◽  
Response Measurement ◽  
Theoretical Predictions

The accuracy of the frequency response measurement obtained using impact excitation and a Fast Fourier Transform based spectrum analyzer has been investigated. It has been shown that with impact excitation, provided the impacts are reproducible and the extraneous noise level is low, the coherence estimates obtained from the analyzer are unity, irrespective of the frequency resolution employed. Hence the H1 (Sxy/Sxx) and H2 (Syy/Sxy*) frequency response function estimates are identical. However, these frequency response function estimates are affected by a bias error caused by inadequate frequency resolution so unity coherence does not necessarily imply accurate results. The results with impact excitation are compared with those obtained using random excitation where both the coherence and frequency response function estimates are affected by bias error. The bias error in the frequency response function estimates with impact excitation is intermediate between that in the H1 and H2 estimates when random excitation is used. The theoretical predictions have been verified by tests on an analogue computer and on a built-up structure.

Rapid Measurement of Modal Properties Using FFT Analyzers With Random Excitation

1986 ◽  
Vol 108 (4) ◽  
pp. 394-398 ◽  
Author(s):  
P. Cawley ◽  
L. G. Rigner
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Frequency Response Function ◽  
Random Excitation ◽  
Nyquist Plot ◽  
Frequency Resolution ◽  
Testing Time ◽  
Rapid Measurement ◽  
Modal Amplitude ◽  
Time Required

The use of a Nyquist plot of the H2 (Syy/Sxy*) frequency response function estimates produced by an FFT based spectrum analyzer with random excitation to obtain modal amplitudes and hence modal constants has been investigated. It has been proved that, irrespective of the frequency resolution used, the H2 estimates always lie on the true modal circle so even at coarse frequency resolution, a circle fitted to these points gives accurate values of modal amplitude. The conventional H1 (Sxy/Sxx) estimates lie inside the true modal circle. Use of the H2 technique results in major savings in the testing time required for a modal survey, particularly when measurements are to be taken at many points on the test structure.

Marital Disharmony among Working Couples in Metropolitan Life: an In-depth Study in Kolkata City

2019 ◽  
Vol 8 (8) ◽  
pp. 72-85
Author(s):  
Nilanjana Ghoshal ◽  
Mst Tania Parveen ◽  
Dr Asraful Alam
Keyword(s):  
Functional Method ◽  
Modern Times ◽  
Metropolitan Cities ◽  
Urban India ◽  
Depth Study ◽  
Working Couples ◽  
Set Up ◽  
Time Required ◽  
The City ◽  
Opposite Gender

In India, traditionally and from time immemorial, marriage has always been a sacred bond for people of this country. The aim of this study is to explain a socially sanctioned sex relationship involving people of two opposite gender whose relationship is expected to endure beyond time required for gestation. The functional method of the study has been set up on the field-based observation to find out the reasons behind rising of marital disharmony among working couples. But the problem is initially in modern times the concept of marriage is gradually taking a different turn between couples. Hence the focus of this paper is to study the various factors giving rise to marital disharmonies among working couples in urban India and how these discords can be solved so that couples can lead a happy harmonious married life ahead. Survey has been done in the city of Kolkata taking people from various walks of life. As Kolkata is one of the major Metropolitan cities of India it was easier to find people belonging to different professions. The result of this study is every marriage brings challenges in life. Maximum working couples are losing attachment with each other as they have lack of time for each other. Bringing work at home, sharing of parenthood, indifference towards each other, lack of adjustments are the causes for which level of disharmony is increasing.

scholarly journals Laboratory Measurements of Light Scattering by Dust Particles

1996 ◽  
Vol 150 ◽  
pp. 409-413
Author(s):  
Patrick P. Combet ◽  
Philippe L. Lamy
Keyword(s):  
Light Scattering ◽  
Laser Beam ◽  
Mie Theory ◽  
Spherical Particles ◽  
Dust Particles ◽  
Laboratory Measurements ◽  
Scattering Function ◽  
Hene Laser ◽  
Set Up ◽  
Good Agreement

AbstractWe have set up an experimental device to optically study the scattering properties of dust particles. Measurements over the 8 — 174° interval of scattering angles are performed on a continuously flowing dust loaded jet illuminated by a polarized red HeNe laser beam. The scattering is averaged over the population of the dust particles in the jet, which can be determined independently, and give the “volume scattering function” for the two directions of polarization directly. While results for spherical particles are in good agreement with Mie theory, those for arbitrary particles show conspicuous deviations.

scholarly journals A Generalized Approach for Evaluating the Mechanical Properties of Polymer Nanocomposites Reinforced with Spherical Fillers

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 830
Author(s):  
Julio Cesar Martinez-Garcia ◽  
Alexandre Serraïma-Ferrer ◽  
Aitor Lopeandía-Fernández ◽  
Marco Lattuada ◽  
Janak Sapkota ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Polymeric Nanocomposites ◽  
Mechanical Reinforcement ◽  
Future Studies ◽  
Three Phase ◽  
Theoretical Predictions ◽  
Filler Network ◽  
New Research ◽  
Good Agreement ◽  
Research Avenue

In this work, the effective mechanical reinforcement of polymeric nanocomposites containing spherical particle fillers is predicted based on a generalized analytical three-phase-series-parallel model, considering the concepts of percolation and the interfacial glassy region. While the concept of percolation is solely taken as a contribution of the filler-network, we herein show that the glassy interphase between filler and matrix, which is often in the nanometers range, is also to be considered while interpreting enhanced mechanical properties of particulate filled polymeric nanocomposites. To demonstrate the relevance of the proposed generalized equation, we have fitted several experimental results which show a good agreement with theoretical predictions. Thus, the approach presented here can be valuable to elucidate new possible conceptual routes for the creation of new materials with fundamental technological applications and can open a new research avenue for future studies.

scholarly journals Simple low dose radiography allows precise lung volume assessment in mice

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Amara Khan ◽  
Andrea Markus ◽  
Thomas Rittmann ◽  
Jonas Albers ◽  
Frauke Alves ◽  
...  
Keyword(s):  
Lung Function ◽  
Whole Body ◽  
Acquisition Time ◽  
Micro Ct ◽  
Lung Volumes ◽  
X Ray ◽  
Promising Tool ◽  
Volume Assessment ◽  
Set Up ◽  
Time Required

AbstractX-ray based lung function (XLF) as a planar method uses dramatically less X-ray dose than computed tomography (CT) but so far lacked the ability to relate its parameters to pulmonary air volume. The purpose of this study was to calibrate the functional constituents of XLF that are biomedically decipherable and directly comparable to that of micro-CT and whole-body plethysmography (WBP). Here, we developed a unique set-up for simultaneous assessment of lung function and volume using XLF, micro-CT and WBP on healthy mice. Our results reveal a strong correlation of lung volumes obtained from radiographic XLF and micro-CT and demonstrate that XLF is superior to WBP in sensitivity and precision to assess lung volumes. Importantly, XLF measurement uses only a fraction of the radiation dose and acquisition time required for CT. Therefore, the redefined XLF approach is a promising tool for preclinical longitudinal studies with a substantial potential of clinical translation.

scholarly journals Residual limb volume fluctuations in transfemoral amputees

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Linda Paternò ◽  
Michele Ibrahimi ◽  
Elisa Rosini ◽  
Giuseppe Menfi ◽  
Vito Monaco ◽  
...  
Keyword(s):  
Physical Activity ◽  
Test Session ◽  
Testing Time ◽  
Residual Limb ◽  
Limb Volume ◽  
Volume Fluctuations ◽  
Exponential Trend ◽  
Prosthesis Removal ◽  
Transfemoral Amputees ◽  
Time Required

AbstractThis study constitutes the first attempt to systematically quantify residual limb volume fluctuations in transfemoral amputees. The study was carried out on 24 amputees to investigate variations due to prosthesis doffing, physical activity, and testing time. A proper experimental set-up was designed, including a 3D optical scanner to improve precision and acceptability by amputees. The first test session aimed at measuring residual limb volume at 7 time-points, with 10 min intervals, after prosthesis doffing. This allowed for evaluating the time required for volume stabilization after prosthesis removal, for each amputee. In subsequent sessions, 16 residual limb scans in a day for each amputee were captured to evaluate volume fluctuations due to prosthesis removal and physical activity, in two times per day (morning and afternoon). These measurements were repeated in three different days, a week apart from each other, for a total of 48 scans for each amputee. Volume fluctuations over time after prosthesis doffing showed a two-term decay exponential trend (R2 = 0.97), with the highest variation in the initial 10 min and an average stabilization time of 30 min. A statistically significant increase in residual limb volume following both prosthesis removal and physical activity was verified. No differences were observed between measures collected in the morning and in the afternoon.Clinical Trials.gov ID: NCT04709367.

Simulating the behaviour of folded cartons during complex packing operations

2006 ◽  
Vol 220 (12) ◽  
pp. 1797-1811 ◽  
Author(s):  
D M Sirkett ◽  
B J Hicks ◽  
C Berry ◽  
G Mullineux ◽  
A J Medland
Keyword(s):  
End Users ◽  
Fundamental Issue ◽  
Trial And Error ◽  
Machine Material ◽  
Packaging Machine ◽  
Set Up ◽  
Fine Tune ◽  
Responsiveness To Change ◽  
Lower Production ◽  
Good Agreement

The folding carton is a widely used packaging solution. Recent European Union packaging legislation has forced carton manufacturers to use lighter-weight grades of carton board. This typically results in a reduction in board stiffness, which can lead to decreased process efficacy or even prevent successful processing. In order to overcome this, end-users lower production rates and fine-tune packaging machine settings for each pack and material. This trial-and-error approach is necessary because the rules relating machine set-up to pack design and material properties are not generally well known. The present study addresses this fundamental issue through the creation of a finite-element computer simulation of carton processing. Mechanical testing was performed to ascertain the key mechanical properties of the carton walls and creases. The carton model was validated against the experimental results and was then subjected to the machine-material interactions that take place during complex packaging operations. The overall approach was validated and the simulation showed good agreement with the physical system. The results of the simulation can be used to determine guidelines relating machine set-up criteria to carton properties. This will improve responsiveness to change and will ultimately allow end-users to process thinner lighter-weight materials more effectively.

Models for New Corrugated and Porous Solar Air Collectors under Transient Operation

2017 ◽  
Vol 42 (1) ◽  
Author(s):  
Qahtan Adnan Abed ◽  
Viorel Badescu ◽  
Adrian Ciocanea ◽  
Iuliana Soriga ◽  
Dorin Bureţea
Keyword(s):  
Climatic Conditions ◽  
Meteorological Conditions ◽  
Bias Error ◽  
First Order ◽  
Solar Air Collector ◽  
Section Surface ◽  
South Eastern Europe ◽  
Main Components ◽  
Theoretical Results ◽  
Good Agreement

AbstractMathematical models have been developed to evaluate the dynamic behavior of two solar air collectors: the first one is equipped with a V-porous absorber and the second one with a U-corrugated absorber. The collectors have the same geometry, cross-section surface area and are built from the same materials, the only difference between them being the absorbers. V-corrugated absorbers have been treated in literature but the V-porous absorbers modeled here have not been very often considered. The models are based on first-order differential equations which describe the heat exchange between the main components of the two types of solar air heaters. Both collectors were exposed to the sun in the same meteorological conditions, at identical tilt angle and they operated at the same air mass flow rate. The tests were carried out in the climatic conditions of Bucharest (Romania, South Eastern Europe). There is good agreement between the theoretical results and experiments. The average bias error was about 7.75 % and 10.55 % for the solar air collector with “V”-porous absorber and with “U”-corrugated absorber, respectively. The collector based on V-porous absorber has higher efficiency than the collector with U-corrugated absorber around the noon of clear days. Around sunrise and sunset, the collector with U-corrugated absorber is more effective.

scholarly journals The European TeleCheck-AF project on remote app-based management of atrial fibrillation during the COVID-19 pandemic: centre and patient experiences

EP Europace ◽  
2021 ◽  
Author(s):  
Monika Gawałko ◽  
David Duncker ◽  
Martin Manninger ◽  
Rachel M J van der Velden ◽  
Astrid N L Hermans ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Care Delivery ◽  
Patient Characteristics ◽  
Patient Experiences ◽  
Af Ablation ◽  
District Hospitals ◽  
Inclusion Rate ◽  
Set Up ◽  
Time Required ◽  
Short Time

Abstract Aims TeleCheck-AF is a multicentre international project initiated to maintain care delivery for patients with atrial fibrillation (AF) during COVID-19 through teleconsultations supported by an on-demand photoplethysmography-based heart rate and rhythm monitoring app (FibriCheck®). We describe the characteristics, inclusion rates, and experiences from participating centres according the TeleCheck-AF infrastructure as well as characteristics and experiences from recruited patients. Methods and results Three surveys exploring centre characteristics (n = 25), centre experiences (n = 23), and patient experiences (n = 826) were completed. Self-reported patient characteristics were obtained from the app. Most centres were academic (64%) and specialized public cardiology/district hospitals (36%). Majority of the centres had AF outpatient clinics (64%) and only 36% had AF ablation clinics. The time required to start patient inclusion and total number of included patients in the project was comparable for centres experienced (56%) or inexperienced in mHealth use. Within 28 weeks, 1930 AF patients were recruited, mainly for remote AF control (31% of patients) and AF ablation follow-up (42%). Average inclusion rate was highest during the lockdown restrictions and reached a steady state at a lower level after easing the restrictions (188 vs. 52 weekly recruited patients). Majority (>80%) of the centres reported no problems during the implementation of the TeleCheck-AF approach. Recruited patients [median age 64 (55–71), 62% male] agreed that the FibriCheck® app was easy to use (94%). Conclusion Despite different health care settings and mobile health experiences, the TeleCheck-AF approach could be set up within an extremely short time and easily used in different European centres during COVID-19.

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