13,955 research outputs found
Bayesian analysis of spatially distorted cosmic signals from Poissonian data
Reconstructing the matter density field from galaxy counts is a problem
frequently addressed in current literature. Two main sources of error are shot
noise from galaxy counts and insufficient knowledge of the correct galaxy
position caused by peculiar velocities and redshift measurement uncertainty.
Here we address the reconstruction problem of a Poissonian sampled log-normal
density field with velocity distortions in a Bayesian way via a maximum a
posteriory method. We test our algorithm on a 1D toy case and find significant
improvement compared to simple data inversion. In particular, we address the
following problems: photometric redshifts, mapping of extended sources in coded
mask systems, real space reconstruction from redshift space galaxy distribution
and combined analysis of data with different point spread functions.Comment: 19 pages, 10 figures, accepte
Measuring dynamic signals with direct sensor-to-microcontroller interfaces applied to a magnetoresistive sensor
This paper evaluates the performance of direct interface circuits (DIC), where the sensor is directly connected to a microcontroller, when a resistive sensor subjected to dynamic changes is measured. The theoretical analysis provides guidelines for the selection of the components taking into account both the desired resolution and the bandwidth of the input signal. Such an analysis reveals that there is a trade-off between the sampling frequency and the resolution of the measurement, and this depends on the selected value of the capacitor that forms the RC circuit together with the sensor resistance. This performance is then experimentally proved with a DIC measuring a magnetoresistive sensor exposed to a magnetic field of different frequencies, amplitudes, and waveforms. A sinusoidal magnetic field up to 1 kHz can be monitored with a resolution of eight bits and a sampling frequency of around 10 kSa/s. If a higher resolution is desired, the sampling frequency has to be lower, thus limiting the bandwidth of the dynamic signal under measurement. The DIC is also applied to measure an electrocardiogram-type signal and its QRS complex is well identified, which enables the estimation, for instance, of the heart rate.Postprint (published version
Frequency-modulated continuous-wave LiDAR compressive depth-mapping
We present an inexpensive architecture for converting a frequency-modulated
continuous-wave LiDAR system into a compressive-sensing based depth-mapping
camera. Instead of raster scanning to obtain depth-maps, compressive sensing is
used to significantly reduce the number of measurements. Ideally, our approach
requires two difference detectors. % but can operate with only one at the cost
of doubling the number of measurments. Due to the large flux entering the
detectors, the signal amplification from heterodyne detection, and the effects
of background subtraction from compressive sensing, the system can obtain
higher signal-to-noise ratios over detector-array based schemes while scanning
a scene faster than is possible through raster-scanning. %Moreover, we show how
a single total-variation minimization and two fast least-squares minimizations,
instead of a single complex nonlinear minimization, can efficiently recover
high-resolution depth-maps with minimal computational overhead. Moreover, by
efficiently storing only data points from measurements of an
pixel scene, we can easily extract depths by solving only two linear equations
with efficient convex-optimization methods
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