1,833 research outputs found
Non-invasive Measurements of Cavity Parameters by Use of Squeezed Vacuum
We propose and experimentally demonstrate a method for non-invasive
measurements of cavity parameters by injection of squeezed vacuum into an
optical cavity. The principle behind this technique is the destruction of the
correlation between upper and lower quantum sidebands with respect to the
carrier frequency when the squeezed field is incident on the cavity. This
method is especially useful for ultrahigh cavities, such as whispering
gallery mode (WGM) cavities, in which absorption and scattering by
light-induced nonlinear processes inhibit precise measurements of the cavity
parameters. We show that the linewidth of a test cavity is measured to be
kHz, which agrees with the classically measured linewidth
of the cavity within the uncertainty ( kHz).Comment: 6 pages, 4 figure
pyPPG: A Python toolbox for comprehensive photoplethysmography signal analysis
Photoplethysmography is a non-invasive optical technique that measures
changes in blood volume within tissues. It is commonly and increasingly used
for in a variety of research and clinical application to assess vascular
dynamics and physiological parameters. Yet, contrary to heart rate variability
measures, a field which has seen the development of stable standards and
advanced toolboxes and software, no such standards and open tools exist for
continuous photoplethysmogram (PPG) analysis. Consequently, the primary
objective of this research was to identify, standardize, implement and validate
key digital PPG biomarkers. This work describes the creation of a standard
Python toolbox, denoted pyPPG, for long-term continuous PPG time series
analysis recorded using a standard finger-based transmission pulse oximeter.
The improved PPG peak detector had an F1-score of 88.19% for the
state-of-the-art benchmark when evaluated on 2,054 adult polysomnography
recordings totaling over 91 million reference beats. This algorithm
outperformed the open-source original Matlab implementation by ~5% when
benchmarked on a subset of 100 randomly selected MESA recordings. More than
3,000 fiducial points were manually annotated by two annotators in order to
validate the fiducial points detector. The detector consistently demonstrated
high performance, with a mean absolute error of less than 10 ms for all
fiducial points. Based on these fiducial points, pyPPG engineers a set of 74
PPG biomarkers. Studying the PPG time series variability using pyPPG can
enhance our understanding of the manifestations and etiology of diseases. This
toolbox can also be used for biomarker engineering in training data-driven
models. pyPPG is available on physiozoo.orgComment: The manuscript was submitted to "Physiological Measurement" on
September 5, 202
Robust peak detection for photoplethysmography signal analysis
Efficient and accurate evaluation of long-term photoplethysmography (PPG)
recordings is essential for both clinical assessments and consumer products. In
2021, the top opensource peak detectors were benchmarked on the Multi-Ethnic
Study of Atherosclerosis (MESA) database consisting of polysomnography (PSG)
recordings and continuous sleep PPG data, where the Automatic Beat Detector
(Aboy) had the best accuracy. This work presents Aboy++, an improved version of
the original Aboy beat detector. The algorithm was evaluated on 100 adult PPG
recordings from the MESA database, which contains more than 4.25 million
reference beats. Aboy++ achieved an F1-score of 85.5%, compared to 80.99% for
the original Aboy peak detector. On average, Aboy++ processed a 1 hour-long
recording in less than 2 seconds. This is compared to 115 seconds (i.e., over
57-times longer) for the open-source implementation of the original Aboy peak
detector. This study demonstrated the importance of developing robust
algorithms like Aboy++ to improve PPG data analysis and clinical outcomes.
Overall, Aboy++ is a reliable tool for evaluating long-term wearable PPG
measurements in clinical and consumer contexts.Comment: 4 pages, 1 figure, 50th Computing in Cardiology conference in
Atlanta, Georgia, USA on 1st - 4th October 202
Photothermal Fluctuations as a Fundamental Limit to Low-Frequency Squeezing in a Degenerate Optical Parametric Amplifier
We study the effect of photothermal fluctuations on squeezed states of light
through the photo-refractive effect and thermal expansion in a degenerate
optical parametric amplifier (OPA). We also discuss the effect of the
photothermal noise in various cases and how to minimize its undesirable
consequences. We find that the photothermal noise in the OPA introduces a
significant amount of noise on phase squeezed beams, making them less than
ideal for low frequency applications such as gravitational wave (GW)
interferometers, whereas amplitude squeezed beams are relatively immune to the
photothermal noise and may represent the best choice for application in GW
interferometers
Hybrid dispersion laser scanner.
Laser scanning technology is one of the most integral parts of today's scientific research, manufacturing, defense, and biomedicine. In many applications, high-speed scanning capability is essential for scanning a large area in a short time and multi-dimensional sensing of moving objects and dynamical processes with fine temporal resolution. Unfortunately, conventional laser scanners are often too slow, resulting in limited precision and utility. Here we present a new type of laser scanner that offers ∼1,000 times higher scan rates than conventional state-of-the-art scanners. This method employs spatial dispersion of temporally stretched broadband optical pulses onto the target, enabling inertia-free laser scans at unprecedented scan rates of nearly 100 MHz at 800 nm. To show our scanner's broad utility, we use it to demonstrate unique and previously difficult-to-achieve capabilities in imaging, surface vibrometry, and flow cytometry at a record 2D raster scan rate of more than 100 kHz with 27,000 resolvable points
Non-linear flexural behaviour of RC columns including bar buckling and fatigue degradation
An advanced fibre-based modelling technique is developed to characterise the non-linear flexural behaviour of rectangular reinforced-concrete (RC) columns by accounting for the influence of inelastic buckling and low-cycle fatigue degradation of vertical reinforcement. The proposed uniaxial material model of reinforcing steel is calibrated using 22 rectangular RC column tests. The influence of inelastic buckling of vertical reinforcement on the non-linear cyclic response of rectangular RC columns is investigated. The calibrated model is capable of accurately predicting the non-linear response of rectangular RC columns up to complete collapse by taking into account the additional failure modes of the RC columns
Knot Floer homology detects fibred knots
Ozsv\'ath and Szab\'o conjectured that knot Floer homology detects fibred
knots in . We will prove this conjecture for null-homologous knots in
arbitrary closed 3--manifolds. Namely, if is a knot in a closed 3--manifold
, is irreducible, and is monic, then is fibred.
The proof relies on previous works due to Gabai, Ozsv\'ath--Szab\'o, Ghiggini
and the author. A corollary is that if a knot in admits a lens space
surgery, then the knot is fibred.Comment: version 4: incorporates referee's suggestions, to appear in
Inventiones Mathematica
Alternative Splicing of P/Q-Type Ca2+ Channels Shapes Presynaptic Plasticity
Alternative splicing of pre-mRNAs is prominent in the mammalian brain, where it is thought to expand proteome diversity. For example, alternative splicing of voltage-gated Ca2+ channel (VGCC) α1 subunits can generate thousands of isoforms with differential properties and expression patterns. However, the impact of this molecular diversity on brain function, particularly on synaptic transmission, which crucially depends on VGCCs, is unclear. Here, we investigate how two major splice isoforms of P/Q-type VGCCs (Cav2.1[EFa/b]) regulate presynaptic plasticity in hippocampal neurons. We find that the efficacy of P/Q-type VGCC isoforms in supporting synaptic transmission is markedly different, with Cav2.1[EFa] promoting synaptic depression and Cav2.1[EFb] synaptic facilitation. Following a reduction in network activity, hippocampal neurons upregulate selectively Cav2.1[EFa], the isoform exhibiting the higher synaptic efficacy, thus effectively supporting presynaptic homeostatic plasticity. Therefore, the balance between VGCC splice variants at the synapse is a key factor in controlling neurotransmitter release and presynaptic plasticity
- …