12,953 research outputs found
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A mission synthesis algorithm for fatigue damage analysis
This paper presents a signal processing based algorithm, the Mildly Nonstationary Mission Synthesis
(MNMS), which produces a short mission signal from long records of experimental data. The
algorithm uses the Discrete Fourier Transform, Orthogonal Wavelet Transform and bump reinsertion
procedures. In order to observe the algorithm effectiveness a fatigue damage case study was
performed for a vehicle lower suspension arm using signals containing tensile and compressive
preloading. The mission synthesis results were compared to the original road data in terms of both the
global signal statistics and the fatigue damage variation as a function of compression ratio. Three
bump reinsertion methods were used and evaluated. The methods differed in the manner in which
bumps (shock events) from different wavelet groups (frequency bands) were synchronised during the
reinsertion process. One method, based on time synchronised section reinsertion, produced the best
results in terms of mission signal kurtosis, crest factor, root-mean-square level and power spectral
density. For improved algorithm performance, bump selection was identified as the main control
parameter requiring optimisation
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A mission synthesis algorithm for editing variable amplitude fatigue signals
This paper presents a wavelet-based fatigue data editing algorithm, known
as Wavelet Bump Extraction (WBE), to summarise long record of fatigue
loadings. The key point of this algorithm is to produce a shorter time
history (mission signal) that retains the majority of the original fatigue
damage whilst preserving cycle sequence information. In WBE, features
or bumps are identified in characteristic frequency bands using the
Daubechiesâ wavelet transform. Comparison of the fatigue life between
the original and mission signals was performed to validate the algorithm.
The fatigue life was predicted using a variable amplitude fatigue damage
model and the results showed a good correlation between the damage
caused by the original and mission signals. Finally, the findings suggest
that WBE is a suitable approach for producing a shortened mission signal for accelerated fatigue testing
A Monte Carlo study of organ and effective doses of cone beam computed tomography (CBCT) scans in radiotherapy
Cone-beam CT (CBCT) scans utilized for image guided radiation therapy (IGRT) procedures have become an essential part of radiotherapy. The aim of this study was to assess organ and effective doses resulting from new CBCT scan protocols (head, thorax, and pelvis) released with a software upgrade of the kV on-board-imager (OBI) system. Influence of the scan parameters that were changed in the new protocols on the patient dose was also investigated. Organ and effective doses for protocols of the new software (V2.5) and a previous version (V1.6) were assessed using Monte Carlo (MC) simulations for the International Commission on Radiological Protection (ICRP) adult male and female reference computational phantoms. The number of projections and the mAs values were increased and the size of the scan field was extended in the new protocols. Influence of these changes on organ and effective doses of the scans was investigated. The OBI system was modelled in EGSnrc/BEAMnrc, and organ doses were estimated using EGSnrc/DOSXYZnrc. The MC model was benchmarked against experimental measurements. Organ doses resulting from the V2.5 protocols were higher than those of V1.6 for organs that were partially or fully inside the scans fields, and increased by (3 to 13)%, (10 to 77)%, and (13 to 21)% for the head, thorax, and pelvis protocols for both phantoms, respectively. As a result, effective doses rose by 14%, 17%, and 16% for the male phantom, and 13%, 18%, and 17% for the female phantom for the three scan protocols, respectively. The scan field extension for the V2.5 protocols contributed significantly in the dose increases, especially for organs that were partially irradiated such as the thyroid in head and thorax scans and colon in the pelvic scan. The contribution of the mAs values and projection numbers was minimal in the dose increases, up to 2.5%. The field size extension plays a major role in improving the treatment output by including more markers in the field of view to match between CBCT and CT images and hence setting up the patient precisely. Therefore, a trade-off between the risk and benefits of CBCT scans should be considered, and the dose increases should be monitored. Several recommendations have been made for optimization of the patient dose involved for IGRT procedures
Cloud cover, cloud liquid water and cloud attenuation at Ka and V bands over equatorial climate
Cloud cover statistics and their diurnal variation have been obtained from in situ and satellite measurements for
three equatorial locations. Cloud liquid water content, 0 °C isotherm height and cloud attenuation have also been
obtained from radiosonde measurement using the so-called Salonen model at Kuala Lumpur (Malaysia). The
results show a strong seasonal variation of cloud cover and cloud liquid water content on the two monsoon
seasons. The Liquid Water Content (LWC) obtained from radiosonde and the Tropical Rainfall Measuring Mission
(TRMM) Microwave Imager (TMI) is higher during the Northeast Monsoon season, which corresponds to the
period of higher percentage cloud cover and high rainfall accumulation. The International Telecommunication
UnionâRegion (ITU-R) model underestimates the cumulative distribution of LWC values at the present station.
The relationship of the cloud attenuation, derived from the profiles of liquid water density and temperature within
the cloud, shows an underestimate by the data obtained from the ITU-R model. The cloud attenuation at Kuala
Lumpur is somewhat underestimated by the ITU-R model up to about 1.2 dB at Ka (30 GHz) and 3.4 dB at V (50
GHz) bands. The results of the specific attenuation can be used for the estimation of cloud attenuation at
microwave and millimetre wave over earth-space paths. The present data are important for planning and design of
satellite communications at Ka and V bands on the Earthâspace path in the equatorial region
Psychometric properties of two Islamic measures among young adults in Kuwait: the Sahin-Francis Scale of Attitude toward Islam and the Sahin Index of Islamic Moral Values
Given the importance of developing reliable and valid measures in the psychology of religion, and recent growing interest in developing empirical studies within an Islamic context, the present study discusses the properties of two specially designed instruments: the Sahin-Francis Scale of Attitude toward Islam and the Sahin Index of Islamic Moral Values. Data were provided by a sample of 1,199 students, selected from secondary schools in six educational districts in Kuwait. The sample comprised 603 males and 596 females; 812 were 17 years of age and 387 were 18 years of age. The data support the internal consistency reliability and construct validity of both instruments and commend them for further research
An experimental validation of the fatigue damaging events extracted using the wavelet bump extraction (WBE) algorithm
This paper describes an experimental validation of the fatigue damaging events that were identified and
extracted using a wavelet-based fatigue data editing technique. This technique, known as the Wavelet Bump
Extraction (WBE) algorithm, is specifically designed to summarise a long record of fatigue variable amplitude
(VA) loading whilst preserving the original load cycle sequence. Using WBE the fatigue damaging events were
identified and extracted in order to produce a mission signal. In order to validate the effectiveness of WBE in
practical applications a VA road load time history that was measured on a road vehicle suspension arm was
taken as a case study. Uniaxial fatigue tests were performed using the original signal, the WBE mission signal
and the individual WBE extracted segments. A mirror polished specimen of SAE 1042 steel was tested using a
servo-hydraulic machine. The fatigue lives measured for these VA loadings were then compared to the fatigue
lives calculated from a VA strain loading fatigue damage model. The results show a good fatigue life
correlation at the coefficient of 0.98 between the prediction and experiment. For the road load time history
considered, the WBE mission signal was found to be only 40% the time duration of the original time history
while maintaining 60% of the fatigue damage according to analytical calculation and 87% according to experimental testing
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Bump extraction algorithm for variable amplitude fatigue loading
This paper presents the development of a fatigue mission synthesis algorithm, called Wavelet Bump Extraction (WBE), for summarising long records of fatigue road load data. This algorithm is used to extract fatigue damaging events or bumps in the record that cause the majority of the fatigue damage, whilst preserving the load cycle sequences. Bumps are identified from characteristic frequency bands in the load spectrum using the 12th order Daubechies wavelet. The bumps are combined to produce a mission signal which has equivalent signal statistics and fatigue damage to the original signal. The WBE accuracy has been evaluated by observing the cycle sequence effects of the bump loadings. The WBE was compared with the time domain fatigue data editing method, so that the effectiveness of WBE can be verified. Using WBE, a substantial compression of the load-time history could be achieved for the purpose of accelerated fatigue tests in the automotive industry
Geometry induced entanglement transitions in nanostructures
We model quantum dot nanostructures using a one-dimensional system of two
interacting electrons. We show that strong and rapid variations may be induced
in the spatial entanglement by varying the nanostructure geometry. We
investigate the position-space information entropy as an indicator of the
entanglement in this system. We also consider the expectation value of the
Coulomb interaction and the ratio of this expectation to the expectation of the
confining potential and their link to the entanglement. We look at the first
derivative of the entanglement and the position-space information entropy to
infer information about a possible quantum phase transition.Comment: 3 pages, 2 figures, to appear in Journal of Applied Physic
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