7,160 research outputs found
Nanoscale resolution interrogation scheme for simultaneous static and dynamic fiber Bragg grating strain sensing
A combined interrogation and signal processing technique which facilitates high-speed simultaneous static and dynamic strain demodulation of multiplexed fiber Bragg grating sensors is described. The scheme integrates passive, interferometric wavelength-demodulation and fast optical switching between wavelength division multiplexer channels with signal extraction via a software lock-in amplifier and fast Fourier transform. Static and dynamic strain measurements with noise floors of 1 nanostrain and 10 nanostrain/sqrt(Hz), between 5 mHz and 2 kHz were obtained. An inverse analysis applied to a cantilever beam set up was used to characterise and verify strain measurements using finite element modeling. By providing distributed measurements of both ultahigh-resolution static and dynamic strain, the proposed scheme will facilitate advanced structural health monitoring
High-speed interferometric FBG interrogator with dynamic and absolute wavelength measurement capability
A passive, interferometric wavelength demodulation technique has been extended to measure the absolute wavelengths of a multiplexed array of fiber Bragg grating sensors. The scheme retains its original strain resolution of 10 nε/√{Hz}. A proof-of-concept interrogation system was able to determine the absolute wavelength of Bragg peaks to within 20 pm (17 με). Static and dynamic Bragg grating strains were accurately demodulated in both absolute and relative wavelength measurement modes. This demonstration indicates that interferometric techniques are able to provide absolute, static and dynamic measurements of strain within a single platform
The effects of stabilizing and destabilizing longitudinal curvature on the structure of turbulent, two-stream mixing layers
The construction and development of the multi-component traversing system and associated control hardware and software are presented. A hydrogen bubble/laser sheet flow visualization technique was developed to visually study the characteristics of the mixing layers. With this technique large-scale rollers arising from the Taylor-Gortler instability and its interaction with the primary Kelvin-Helmholtz structures can be studied
Pulsar Spin--Velocity Alignment: Further Results and Discussion
The reported alignment between the projected spin-axes and proper motion
directions of pulsars is revisited in the light of new data from Jodrell Bank
and Effelsberg. The present investigation uses 54 pulsars, the largest to date
sample of pulsars with proper-motion and absolute polarisation, to study this
effect. Our study has found strong evidence for pulsar spin-velocity alignment,
excluding that those two vectors are completely uncorrelated, with >99%
confidence. Although we cannot exclude the possibility of orthogonal
spin-velocity configurations, comparison of the data with simulations shows
that the scenario of aligned vectors is more likely than that of the orthogonal
case. Moreover, we have determined the spread of velocities that a spin-aligned
and spin-orthogonal distribution of kicks must have to produce the observed
distribution of spin-velocity angle offsets. If the observed distribution of
spin-velocity offset angles is the result of spin-aligned kicks, then we find
that the distribution of kick-velocity directions must be broad with
{\sigma}_v~30\degree if the orthogonal-kick scenario is assumed, then the
velocity distribution is much narrower with {\sigma}_v<10\degree. Finally, in
contrast to previous studies, we have performed robustness tests on our data,
in order to determine whether our conclusions are the result of a statistical
and/or systematic bias. The conclusion of a correlation between the spin and
velocity vectors is independent of a bias introduced by subsets in the total
sample. Moreover, we estimate that the observed alignment is robust to within
10% systematic uncertainties on the determination of the spin-axis direction
from polarisation data.Comment: 20 pages, 7 figures, 1 Table, accepted in MNRA
Recommended from our members
The Role of Aspect in the Composition of Temporal Adverbial Clauses with Adverbs of Quantification
Intellectual Property for New Entrepreneurs
Abstract – New entrepreneurs, regardless of age, encounter several barriers regarding intellectual property. My research posits that new entrepreneurs are burdened by both informational barriers and lack of resources. A data driven analysis of this problem produced an easy to comprehend guide targeted to new entrepreneurs. This paper presents a subjective guide for entrepreneurs that details patents, trademarks, copyrights, and licensing
Evidence on the Long Shadow of Poor Mental Health across Three Generations
Individuals suffering from mental health problems are often severely limited in their social and economic functioning. Mental health problems can develop early in life, are frequently chronic in nature, and have an established hereditary component. The extent to which mental illness runs in families could therefore help explain the widely discussed intergenerational transmission of socioeconomic disadvantage. Using data from three generations contained in the 1970 British Cohort Study, we estimate the intergenerational correlation of mental health between mothers, their children, and their grandchildren. We find that the intergenerational correlation in mental health is about 0.2, and that the probability of feeling depressed is 63 percent higher for children whose mothers reported the same symptom 20 years earlier. Moreover, grandmother and grandchild mental health are strongly correlated, but this relationship appears to work fully through the mental health of the parent. Using grandmother mental health as an instrument for maternal mental health in a model of grandchild mental health confirms the strong intergenerational correlation. We also find that maternal and own mental health are strong predictors of adulthood socioeconomic outcomes. Even after controlling for parental socioeconomic status, own educational attainment, and own mental health (captured in childhood and adulthood), our results suggest that a one standard deviation reduction in maternal mental health reduces household income for their adult offspring by around 2 percent.intergenerational transmission, mobility, mental health, economic outcomes
Pulsar Spin-Velocity Alignment: Kinematic Ages, Birth Periods and Braking Indices
This paper presents a detailed investigation of the dependence of pulsar
spin-velocity alignment, which has been observed for a sample of 58 pulsars, on
pulsar age. At first, our study considers only pulsar characteristic ages,
resulting in no change in the degree of correlation as a function of age, up to
at least 100 Myr. Subsequently, we consider a more reliable estimate of pulsar
age, the kinematic age, assuming that pulsars are born near the Galactic plane.
We derive kinematic ages for 52 pulsars, based on the measured pulsar proper
motions and positions, by modelling the trajectory of the pulsars in a Galactic
potential. The sample of 52 pulsar kinematic ages constitutes the largest
number of independently estimated pulsar ages to date. Using only the 33 most
reliable kinematic ages from our simulations, we revisit the evolution of spin-
velocity alignment, this time as a function of kinematic age. We find that the
strong correlation seen in young pulsars is completely smeared out for pulsars
with kinematic ages above 10 Myr, a length of time beyond which we expect the
gravitational pull of the Galaxy to have a significant effect on the directions
of pulsar velocities. In the discussion, we investigate the impact of large
distance uncertainties on the reliability of the calculated kinematic ages.
Furthermore, we present a detailed investigation of the implications of our
revised pulsar ages for the braking-index and birth-period distributions.
Finally, we discuss the predictions of various SN-kick mechanisms and their
compatibility with our results.Comment: 24 pages, 19 figures, MNRAS accepte
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