165 research outputs found
Macroscopic fluctuations theory of aerogel dynamics
We consider the thermodynamic potential describing the macroscopic
fluctuation of the current and local energy of a general class of Hamiltonian
models including aerogels. We argue that this potential is neither analytic nor
strictly convex, a property that should be expected in general but missing from
models studied in the literature. This opens the possibility of describing in
terms of a thermodynamic potential non-equilibrium phase transitions in a
concrete physical context. This special behaviour of the thermodynamic
potential is caused by the fact that the energy current is carried by particles
which may have arbitrary low speed with sufficiently large probability.Comment: final versio
Wearable Sleep Technology in Clinical and Research Settings
The accurate assessment of sleep is critical to better understand and evaluate its role in health and disease. The boom in wearable technology is part of the digital health revolution and is producing many novel, highly sophisticated and relatively inexpensive consumer devices collecting data from multiple sensors and claiming to extract information about users' behaviors, including sleep. These devices are now able to capture different biosignals for determining, for example, HR and its variability, skin conductance, and temperature, in addition to activity. They perform 24/7, generating overwhelmingly large data sets (big data), with the potential of offering an unprecedented window on users' health. Unfortunately, little guidance exists within and outside the scientific sleep community for their use, leading to confusion and controversy about their validity and application. The current state-of-the-art review aims to highlight use, validation and utility of consumer wearable sleep-trackers in clinical practice and research. Guidelines for a standardized assessment of device performance is deemed necessary, and several critical factors (proprietary algorithms, device malfunction, firmware updates) need to be considered before using these devices in clinical and sleep research protocols. Ultimately, wearable sleep technology holds promise for advancing understanding of sleep health; however, a careful path forward needs to be navigated, understanding the benefits and pitfalls of this technology as applied in sleep research and clinical sleep medicine
Sub-femto-g free fall for space-based gravitational wave observatories: LISA pathfinder results
We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2 ± 0.1 fm s−2/√Hz or (0.54 ± 0.01) × 10−15 g/√Hz, with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8 ± 0.3) fm/√Hz, about 2 orders of magnitude better than requirements. At f ≤ 0.5 mHz we observe a low-frequency tail that stays below 12 fm s−2/√Hz down to 0.1 mHz. This performance would allow for a space-based gravitational wave
observatory with a sensitivity close to what was originally foreseen for LISA
Micrometeoroid Events in LISA Pathfinder
The zodiacal dust complex, a population of dust and small particles that
pervades the Solar System, provides important insight into the formation and
dynamics of planets, comets, asteroids, and other bodies. Here we present a new
set of data obtained using a novel technique: direct measurements of momentum
transfer to a spacecraft from individual particle impacts. This technique is
made possible by the extreme precision of the instruments flown on the LISA
Pathfinder spacecraft, a technology demonstrator for a future space-based
gravitational wave observatory that operated near the first Sun-Earth Lagrange
point from early 2016 through Summer of 2017. Using a simple model of the
impacts and knowledge of the control system, we show that it is possible to
detect impacts and measure properties such as the transferred momentum (related
to the particle's mass and velocity), direction of travel, and location of
impact on the spacecraft. In this paper, we present the results of a systematic
search for impacts during 4348 hours of Pathfinder data. We report a total of
54 candidates with momenta ranging from 0.2 to
230. We furthermore make a comparison of these candidates
with models of micrometeoroid populations in the inner solar system including
those resulting from Jupiter-family comets, Oort-cloud comets, Hailey-type
comets, and Asteroids. We find that our measured population is consistent with
a population dominated by Jupiter-family comets with some evidence for a
smaller contribution from Hailey-type comets. This is in agreement with
consensus models of the zodiacal dust complex in the momentum range sampled by
LISA Pathfinder.Comment: 22 pages, 14 figures, accepted in Ap
The risk stratification of adverse neonatal outcomes in women with gestational diabetes (STRONG) study
Aims: To assess the risk of adverse neonatal outcomes in women with gestational diabetes (GDM) by identifying subgroups of women at higher risk to recognize the characteristics most associated with an excess of risk. Methods: Observational, retrospective, multicenter study involving consecutive women with GDM. To identify distinct and homogeneous subgroups of women at a higher risk, the RECursive Partitioning and AMalgamation (RECPAM) method was used. Overall, 2736 pregnancies complicated by GDM were analyzed. The main outcome measure was the occurrence of adverse neonatal outcomes in pregnancies complicated by GDM. Results: Among study participants (median age 36.8 years, pre-gestational BMI 24.8 kg/m2), six miscarriages, one neonatal death, but no maternal death was recorded. The occurrence of the cumulative adverse outcome (OR 2.48, 95% CI 1.59–3.87), large for gestational age (OR 3.99, 95% CI 2.40–6.63), fetal malformation (OR 2.66, 95% CI 1.00–7.18), and respiratory distress (OR 4.33, 95% CI 1.33–14.12) was associated with previous macrosomia. Large for gestational age was also associated with obesity (OR 1.46, 95% CI 1.00–2.15). Small for gestational age was associated with first trimester glucose levels (OR 1.96, 95% CI 1.04–3.69). Neonatal hypoglycemia was associated with overweight (OR 1.52, 95% CI 1.02–2.27) and obesity (OR 1.62, 95% CI 1.04–2.51). The RECPAM analysis identified high-risk subgroups mainly characterized by high pre-pregnancy BMI (OR 1.68, 95% CI 1.21–2.33 for obese; OR 1.38 95% CI 1.03–1.87 for overweight). Conclusions: A deep investigation on the factors associated with adverse neonatal outcomes requires a risk stratification. In particular, great attention must be paid to the prevention and treatment of obesity
The Relationship Between Diagnosed Burnout and Sleep Measured by Activity Trackers:Four Longitudinal Case Studies
Systematic review of the validity and reliability of consumer-wearable activity trackers
Abstract Background Consumer-wearable activity trackers are electronic devices used for monitoring fitness- and other health-related metrics. The purpose of this systematic review was to summarize the evidence for validity and reliability of popular consumer-wearable activity trackers (Fitbit and Jawbone) and their ability to estimate steps, distance, physical activity, energy expenditure, and sleep. Methods Searches included only full-length English language studies published in PubMed, Embase, SPORTDiscus, and Google Scholar through July 31, 2015. Two people reviewed and abstracted each included study. Results In total, 22 studies were included in the review (20 on adults, 2 on youth). For laboratory-based studies using step counting or accelerometer steps, the correlation with tracker-assessed steps was high for both Fitbit and Jawbone (Pearson or intraclass correlation coefficients (CC) > =0.80). Only one study assessed distance for the Fitbit, finding an over-estimate at slower speeds and under-estimate at faster speeds. Two field-based studies compared accelerometry-assessed physical activity to the trackers, with one study finding higher correlation (Spearman CC 0.86, Fitbit) while another study found a wide range in correlation (intraclass CC 0.36–0.70, Fitbit and Jawbone). Using several different comparison measures (indirect and direct calorimetry, accelerometry, self-report), energy expenditure was more often under-estimated by either tracker. Total sleep time and sleep efficiency were over-estimated and wake after sleep onset was under-estimated comparing metrics from polysomnography to either tracker using a normal mode setting. No studies of intradevice reliability were found. Interdevice reliability was reported on seven studies using the Fitbit, but none for the Jawbone. Walking- and running-based Fitbit trials indicated consistently high interdevice reliability for steps (Pearson and intraclass CC 0.76–1.00), distance (intraclass CC 0.90–0.99), and energy expenditure (Pearson and intraclass CC 0.71–0.97). When wearing two Fitbits while sleeping, consistency between the devices was high. Conclusion This systematic review indicated higher validity of steps, few studies on distance and physical activity, and lower validity for energy expenditure and sleep. The evidence reviewed indicated high interdevice reliability for steps, distance, energy expenditure, and sleep for certain Fitbit models. As new activity trackers and features are introduced to the market, documentation of the measurement properties can guide their use in research settings
LISA Pathfinder: OPD loop characterisation
The optical metrology system (OMS) of the LISA Pathfinder mission is measuring the distance between two free-floating test masses with unprecedented precision. One of the four OMS heterodyne interferometers reads out the phase difference between the reference and the measurement laser beam. This phase from the reference interferometer is common to all other longitudinal interferometer read outs and therefore subtracted. In addition, the phase is fed back via the digital optical pathlength difference (OPD) control loop to keep it close to zero. Here, we analyse the loop parameters and compare them to on-ground measurement results
LISA Pathfinder: Understanding DWS noise performance for the LISA mission
ESA's L3 Laser Interferometer Space Antenna (LISA) mission contains a mechanism to compensate for out-of-plane angles between the received and emitted beams of the three satellites. Depending on the configuration of this Point-Ahead Angle Mechanism (PAAM) it is expected to contribute readout noise through Differential Wavefront Sensing (DWS). This was investigated with LISA Pathfinder (LPF) through a dedicated investigation. One of the two free-falling test masses was rotated via the on-board electrostatic actuators while the resulting angular noise in the differential interferometer between the two test masses was measured. For angles between −250 μrad to 250 μrad and corresponding contrast in the range of 59.4 % to 97.9 % an increased spectral density was found. The differential displacement noise remains almost unchanged for these misalignments.The Albert-Einstein-Institut acknowledges the support of the German Space Agency, DLR. The work is supported by the Federal Ministry for Economic Affairs and Energy based on a resolution of the German Bundestag (FKZ 50OQ0501 and FKZ 50OQ1601)
LISA Pathfinder closed-loop analysis: a model breakdown of the in-loop observables
This paper describes a methodology to analyze, in the frequency domain, the steady-state control performances of the LISA Pathfinder mission. In particular, it provides a technical framework to give a comprehensive understanding of the spectra of all the degrees of freedom by breaking them down into their various physical origins, hence bringing out the major contributions of the control residuals. A reconstruction of the measured in-loop output, extracted from a model of the closed-loop system, is shown as an instance to illustrate the potential of such a model breakdown of the data
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