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

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 Daubechies’ 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

Arithmetic properties of eigenvalues of generalized Harper operators on graphs

Let \Qbar denote the field of complex algebraic numbers. A discrete group $G$ is said to have the $\sigma$-multiplier algebraic eigenvalue property, if for every matrix $A$ with entries in the twisted group ring over the complex algebraic numbers M_d(\Qbar(G,\sigma)), regarded as an operator on $l^2(G)^d$, the eigenvalues of $A$ are algebraic numbers, where $\sigma$ is an algebraic multiplier. Such operators include the Harper operator and the discrete magnetic Laplacian that occur in solid state physics. We prove that any finitely generated amenable, free or surface group has this property for any algebraic multiplier $\sigma$. In the special case when $\sigma$ is rational ($\sigma^n$=1 for some positive integer $n$) this property holds for a larger class of groups, containing free groups and amenable groups, and closed under taking directed unions and extensions with amenable quotients. Included in the paper are proofs of other spectral properties of such operators.Comment: 28 pages, latex2e, paper revise

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

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

Observational evidence for the shrinking of bright maser spots

The nature of maser emission means that the apparent angular size of an individual maser spot is determined by the amplification process as well as by the instrinsic size of the emitting cloud. Highly sensitive MERLIN radio interferometry images spatially and spectrally resolve water maser clouds around evolved stars. We measured the properties of clouds around the red supergiant S Per and the AGB stars IK Tau, RT Vir, U Her and U Ori, to test maser beaming theory. Spherical clouds are expected to produce an inverse relationship between maser intensity and apparent size, which would not be seen from cylindrical or slab-like regions. We analysed the maser properties, in order to estimate the saturation state, and investigated the variation of observed spot size with intensity and across the spectral line profiles. Circumstellar masers emanate from discrete clouds from about one to 20 AU in diameter depending on the star. Most of the maser features have negative excitation temperatures close to zero and modest optical depths, showing that they are mainly unsaturated. Around S Per and (at most epochs) RT Vir and IK Tau, the maser component size shrinks with increasing intensity. In contrast, the masers around U Ori and U Her tend to increase in size, with a larger scatter. The water masers from S Per, RT Vir and IK Tau are mainly beamed into spots with an observed angular size much smaller than the emitting clouds and smallest of all at the line peaks. This suggests that the masers are amplification-bounded, emanating from approximately spherical clouds. Many of the masers around U Her and U Ori have apparent sizes which are more similar to the emitting clouds and have less or no dependence on intensity, suggesting that these masers are matter-bounded. This is consistent with an origin in flattened clouds and these two stars have shown other behaviour indicating the presence of shocks.Comment: 17 pages, 26 figure files, accepted by A&A 2010 Oct 2

Mapping CS in Starburst Galaxies: Disentangling and Characterising Dense Gas

Aims. We observe the dense gas tracer CS in two nearby starburst galaxies to determine how the conditions of the dense gas varies across the circumnuclear regions in starburst galaxies. Methods. Using the IRAM-30m telescope, we mapped the distribution of the CS(2-1) and CS(3-2) lines in the circumnuclear regions of the nearby starburst galaxies NGC 3079 and NGC 6946. We also detected the formaldehyde (H2CO) and methanol (CH3OH) in both galaxies. We marginally detect the isotopologue C34S. Results. We calculate column densities under LTE conditions for CS and CH3OH. Using the detections accumulated here to guide our inputs, we link a time and depth dependent chemical model with a molecular line radiative transfer model; we reproduce the observations, showing how conditions where CS is present are likely to vary away from the galactic centres. Conclusions. Using the rotational diagram method for CH3OH, we obtain a lower limit temperature of 14 K. In addition to this, by comparing the chemical and radiative transfer models to observations, we determine the properties of the dense gas as traced by CS (and CH3OH). We also estimate the quantity of the dense gas. We find that, provided that there are a between 10^5 and 10^6 dense cores in our beam, for both target galaxies, emission of CS from warm (T = 100 - 400 K), dense (n(H2) = 10^5-6 cm-3) cores, possibly with a high cosmic ray ionisation rate (zeta = 100 zeta0) best describes conditions for our central pointing. In NGC 6946, conditions are generally cooler and/or less dense further from the centre, whereas in NGC 3079, conditions are more uniform. The inclusion of shocks allows for more efficient CS formation, leading to an order of magnitude less dense gas being required to replicate observations in some cases.Comment: 14 pages, 10 figures, accepted to A&

What kind of shoes does a social worker wear? A content analysis of four occupational prototypes

Evidence suggests that occupational prototypes have an impact on career decisions, through the mechanism of self-to-prototype matching, yet the literature provides scant information about the nature of these occupational prototypes. This study examines the prototypes of four common occupational choices of psychology students in the UK (social worker, primary school teacher, occupational psychologist and clinical psychologist). Data were gathered through four focus groups (N=24) and were analysed with a quantitative content analysis to produce descriptions of the four occupational prototypes. It was found that the occupational prototypes were detailed and multi-dimensional, incorporating a wide range of features not directly related to the job itself including information about clothing, leisure activities and home décor. Implications for career development theory and career practice are discussed

Ranking Significant Discrepancies in Clinical Reports

Medical errors are a major public health concern and a leading cause of death worldwide. Many healthcare centers and hospitals use reporting systems where medical practitioners write a preliminary medical report and the report is later reviewed, revised, and finalized by a more experienced physician. The revisions range from stylistic to corrections of critical errors or misinterpretations of the case. Due to the large quantity of reports written daily, it is often difficult to manually and thoroughly review all the finalized reports to find such errors and learn from them. To address this challenge, we propose a novel ranking approach, consisting of textual and ontological overlaps between the preliminary and final versions of reports. The approach learns to rank the reports based on the degree of discrepancy between the versions. This allows medical practitioners to easily identify and learn from the reports in which their interpretation most substantially differed from that of the attending physician (who finalized the report). This is a crucial step towards uncovering potential errors and helping medical practitioners to learn from such errors, thus improving patient-care in the long run. We evaluate our model on a dataset of radiology reports and show that our approach outperforms both previously-proposed approaches and more recent language models by 4.5% to 15.4%.Comment: ECIR 2020 (short

Enhancement of quasiparticle recombination in Ta and Al superconductors by implantation of magnetic and nonmagnetic atoms

The quasiparticle recombination time in superconducting films, consisting of the standard electron-phonon interaction and a yet to be identified low temperature process, is studied for different densities of magnetic and nonmagnetic atoms. For both Ta and Al, implanted with Mn, Ta and Al, we observe an increase of the recombination rate. We conclude that the enhancement of recombination is not due to the magnetic moment, but arises from an enhancement of disorder.Comment: 4 pages, 4 figure