4,010 research outputs found
Non-destructive testing of carbon reinforced plastics by means of phase retrieval
In this work, the SLM-based phase retrieval system will be used to inspect
carbon reinforced plastics samples (CFRP) under applying a thermal load. For
this purpose, the system is used to capture a sequence of 8 spatially separated
recording planes, where the distance between subsequent planes equals 2 mm. For
detecting the hidden failures two sets of intensity observations are recorded.
The first set for the initial state and the second set is captured after
applying the load. To recover the phase information associated with the two
states, the captured intensities have been subjected to an iterative algorithm
based on the method of generalized projection.Comment: Conf. Speckle 201
Accurate evaluation of the Kochin function for added resistance using a high-order finite difference-based seakeeping code
Implementation of the far-field method for calculation of added resistance using a high order finite-difference approximation on overlapping grids
Missing at random assumption made more plausible: evidence from the 1958 British birth cohort
Objective:
Non-response is unavoidable in longitudinal surveys. The consequences are lower statistical power
and the potential for bias. We implemented a systematic data-driven approach to identify predictors
of non-response in the National Child Development Study (NCDS; 1958 British birth cohort). Such
variables can help make the missing at random assumption more plausible, which has implications for
the handling of missing data. /
Study Design and Setting:
We identified predictors of non-response using data from the 11 sweeps (birth to age 55) of the NCDS
(n = 17,415), employing parametric regressions and the LASSO for variable selection. /
Results:
Disadvantaged socio-economic background in childhood, worse mental health and lower cognitive
ability in early life, and lack of civic and social participation in adulthood were consistently associated
with non-response. Using this information, along with other data from NCDS, we were able to replicate
the “population distribution” of educational attainment and marital status (derived from external
data), and the original distributions of key early life characteristics. /
Conclusion:
The identified predictors of non-response have the potential to improve the plausibility of the missing
at random assumption. They can be straightforwardly used as “auxiliary variables” in analyses with
principled methods to reduce bias due to missing data
The role of frequency and impedance contrasts in bandgap closing and formation patterns of axially-vibrating phononic crystals
Bandgaps, or frequency ranges of forbidden wave propagation, are a hallmark
of Phononic Crystals (PnCs). Unlike their lattice counterparts, PnCs taking the
form of continuous structures exhibit an infinite number of bandgaps of varying
location, bandwidth, and distribution along the frequency spectrum.~While these
bandgaps are commonly predicted from benchmark tools such as the Bloch-wave
theory, the conditions that dictate the patterns associated with bandgap
symmetry, attenuation, or even closing in multi-bandgap PnCs remain an
enigma.~In this work, we establish these patterns in one-dimensional rods
undergoing longitudinal motion via a canonical transfer-matrix-based
approach.~In doing so, we connect the conditions underpinning bandgap emergence
and closing to their physical origins in the context of the Bragg condition
(for infinite media) and natural resonances (for finite counterparts).~The
developed framework uniquely characterizes individual bandgaps within a larger
dispersion spectrum regardless of their parity (i.e., odd vs even bandgaps) or
location (low vs high-frequency), by exploiting dimensionless constants of the
PnC unit cell which quantify the different contrasts between its constitutive
layers. These developments are detailed for a bi-layered PnC and then
generalized for a PnC of any number of layers by increasing the model
complexity. We envision this mathematical development to be a future standard
for the development of hierarchically-structured PnCs with prescribed and
finely tailored bandgap profiles
A high-order finite-difference solver for the linearised potential flow wave resistance problem on curvilinear overset grids
A high-order finite-difference linear seakeeping solver tool for calculation of added resistance in waves
Two-Stage Maximum Likelihood Estimation (TSMLE) for MT-CDMA Signals in the Indoor Environment
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