Atomic clocks are vital in a wide array of technologies and experiments, including tests of fundamental physics
. Clocks operating at optical frequencies have now demonstrated fractional stability ...and reproducibility at the 10
level, two orders of magnitude beyond their microwave predecessors
. Frequency ratio measurements between optical clocks are the basis for many of the applications that take advantage of this remarkable precision. However, the highest reported accuracy for frequency ratio measurements has remained largely unchanged for more than a decade
. Here we operate a network of optical clocks based on
Al
(ref.
),
Sr (ref.
) and
Yb (ref.
), and measure their frequency ratios with fractional uncertainties at or below 8 × 10
. Exploiting this precision, we derive improved constraints on the potential coupling of ultralight bosonic dark matter to standard model fields
. Our optical clock network utilizes not just optical fibre
, but also a 1.5-kilometre free-space link
. This advance in frequency ratio measurements lays the groundwork for future networks of mobile, airborne and remote optical clocks that will be used to test physical laws
, perform relativistic geodesy
and substantially improve international timekeeping
.
Vibrio cholerae infections cluster in households. This study's objective was to quantify the relative contribution of direct, within-household exposure (for example, via contamination of household ...food, water, or surfaces) to endemic cholera transmission. Quantifying the relative contribution of direct exposure is important for planning effective prevention and control measures.
Symptom histories and multiple blood and fecal specimens were prospectively collected from household members of hospital-ascertained cholera cases in Bangladesh from 2001-2006. We estimated the probabilities of cholera transmission through 1) direct exposure within the household and 2) contact with community-based sources of infection. The natural history of cholera infection and covariate effects on transmission were considered. Significant direct transmission (p-value<0.0001) occurred among 1414 members of 364 households. Fecal shedding of O1 El Tor Ogawa was associated with a 4.9% (95% confidence interval: 0.9%-22.8%) risk of infection among household contacts through direct exposure during an 11-day infectious period (mean length). The estimated 11-day risk of O1 El Tor Ogawa infection through exposure to community-based sources was 2.5% (0.8%-8.0%). The corresponding estimated risks for O1 El Tor Inaba and O139 infection were 3.7% (0.7%-16.6%) and 8.2% (2.1%-27.1%) through direct exposure, and 3.4% (1.7%-6.7%) and 2.0% (0.5%-7.3%) through community-based exposure. Children under 5 years-old were at elevated risk of infection. Limitations of the study may have led to an underestimation of the true risk of cholera infection. For instance, available covariate data may have incompletely characterized levels of pre-existing immunity to cholera infection. Transmission via direct exposure occurring outside of the household was not considered.
Direct exposure contributes substantially to endemic transmission of symptomatic cholera in an urban setting. We provide the first estimate of the transmissibility of endemic cholera within prospectively-followed members of households. The role of direct transmission must be considered when planning cholera control activities.
Dynamic vapor microextraction (DVME) is a headspace concentration method that can be used to collect ignitable liquid (IL) from fire debris onto chilled adsorbent capillaries. Unlike passive ...headspace concentration onto activated carbon strips (ACSs) that must be eluted with a toxic solvent (carbon disulfide), DVME employs a relatively benign solvent (acetone) to recover the adsorbed IL residue, and each headspace collection is monitored for breakthrough. Here, for the first time, we extend DVME to casework containers while exploring a realistic range of oven temperatures and collection volumes. We investigated metal cans sealed with friction lids (container 1), metal cans sealed within polymer bags (container 2), and glass jars sealed with two-piece lids (container 3). Without additional containment, container 1 was found to leak so excessively that flow through the capillary was unreliable. Therefore, for containers 2 and 3 only, we determined the total number of target compounds collected from 50% weathered gasoline for oven temperatures from 54 °C to 96 °C and collection volumes from 47 standard cubic centimeters (scc) to 90 scc. Only high-volatility species with retention times (tR)< n-decane on a non-polar column were recovered from polymer bags, whereas headspace concentration from glass jars led to the recovery of target compounds across the entire volatility range. DVME at 90 °C from 2-mL containers showed that the presence of polymer bag material leads to IL vapor losses, particularly for low-volatility species with tR> n-decane. DVME was strongly influenced by the casework container, whereas oven temperature and collection volume had a minor influence for the IL samples explored here.
•Dynamic vapor microextraction (DVME) is a low flow headspace concentration method.•DVME cannot be implemented with metal cans with friction lids due to leaks.•DVME recovered more target compounds from glass jars than polymer evidence bags.•Polymer bag material led to vapor loss, particularly for low-volatility species.
Despite seasonal cholera outbreaks in Bangladesh, little is known about the relationship between environmental conditions and cholera cases. We seek to develop a predictive model for cholera ...outbreaks in Bangladesh based on environmental predictors. To do this, we estimate the contribution of environmental variables, such as water depth and water temperature, to cholera outbreaks in the context of a disease transmission model. We implement a method which simultaneously accounts for disease dynamics and environmental variables in a Susceptible-Infected-Recovered-Susceptible (SIRS) model. The entire system is treated as a continuous-time hidden Markov model, where the hidden Markov states are the numbers of people who are susceptible, infected or recovered at each time point, and the observed states are the numbers of cholera cases reported. We use a Bayesian framework to fit this hidden SIRS model, implementing particle Markov chain Monte Carlo methods to sample from the posterior distribution of the environmental and transmission parameters given the observed data. We test this method using both simulation and data from Mathbaria, Bangladesh. Parameter estimates are used to make short-term predictions that capture the formation and decline of epidemic peaks. We demonstrate that our model can successfully predict an increase in the number of infected individuals in the population weeks before the observed number of cholera cases increases, which could allow for early notification of an epidemic and timely allocation of resources.
We use frequency-comb-based optical two-way time-frequency transfer (O-TWTFT) to measure the optical frequency ratio of state-of-the-art ytterbium and strontium optical atomic clocks separated by a ...1.5-km open-air link. Our free-space measurement is compared to a simultaneous measurement acquired via a noise-cancelled fiber link. Despite nonstationary, ps-level time-of-flight variations in the free-space link, ratio measurements obtained from the two links, averaged over 30.5 hours across six days, agree to 6×10^{−19}, showing that O-TWTFT can support free-space atomic clock comparisons below the 10^{−18} level.
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CMK, CTK, FMFMET, NUK, UL
Decision Tree for Key Comparisons Possolo, Antonio; Koepke, Amanda; Newton, David ...
Journal of research of the National Institute of Standards and Technology,
01/2021, Volume:
126
Journal Article
Open access
This contribution describes a Decision Tree intended to guide the
selection of statistical models and data reduction procedures in key
comparisons (KCs). The Decision Tree addresses a specific need ...of
the Inorganic Analysis Working Group (IAWG) of the Consultative
Committee (CC) for Amount of Substance, Metrology in Chemistry and
Biology (CCQM), of the International Committee for Weights and
Measures (CIPM), and it is likely to address similar needs of other
working groups and consultative committees.
Because the portfolio of KCs previously organized by the CCQM-IAWG
affords a full range of opportunities to demonstrate the
capabilities of the Decision Tree, the majority of the illustrative
examples of application of the Decision Tree are from this working
group. However, the Decision Tree is widely applicable in other
areas of metrology, as illustrated in examples of application to
measurements of radionuclides and of the efficiency of a thermistor
power sensor.
The Decision Tree is intended for use after choices will have been
made about the measurement results that qualify for inclusion in the
calculation of the key comparison reference value (KCRV), and about
the measurement results for which degrees of equivalence should be
produced. Both these choices should be based on substantive
considerations, not on purely statistical criteria. However, the
Decision Tree does not require that the measurement results selected
for either purpose be mutually consistent.
The Decision Tree should be used as a guide, not as the sole and
autonomous determinant of the model that should be selected for the
measurement results obtained in a KC, or of the procedure that
should be employed to reduce these results. The scientists running
the KCs ultimately have the freedom and responsibility to make the
corresponding choices that they deem most appropriate and that best
fit the purpose of each KC.
The Decision Tree involves three statistical tests, and comprises
five terminal leaves, which correspond to as many alternative ways
in which the KCRV, its associated uncertainty, and the degrees of
equivalence (DoEs) may be computed.
This contribution does not purport to suggest that any of the KCRVs,
associated uncertainties, or DoEs, presented in previously approved
final reports issued by working groups of the CCs should be
modified. Neither do the alternative results question existing,
demonstrated calibration and measurement capabilities (CMCs), nor do
they support any new CMCs.
A generative adversarial network (GAN) is an artificial neural network with a
distinctive training architecture, designed to createexamples that faithfully reproduce
a target distribution. GANs have ...recently had particular success in applications
involvinghigh-dimensional distributions in areas such as image processing. Little work
has been reported for low dimensions, where properties of GANs may be better identified
and understood. We studied GAN performance in simulated low-dimensional settings,
allowing us totransparently assess effects of target distribution complexity and
training data sample size on GAN performance in a simpleexperiment. This experiment
revealed two important forms of GAN error, tail underfilling and bridge bias, where the
latter is analogousto the tunneling observed in high-dimensional GANs.
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•A headspace concentration method was evaluated with simulated fire debris.•Sensitivity analysis identified important instrument settings.•Capillary temperature did not affect ...performance, so design can be simplified.•Water content of the debris did not affect performance.
Dynamic vapor microextraction (DVME) is a potential method for the extraction and concentration of ignitable liquid (IL) residue in fire debris. This low flow rate, purge-and-trap headspace concentration method collects IL vapors onto a chilled adsorbent capillary and recovers them by elution with acetone. As an emerging method for fire debris analysis, the sensitivity of DVME performance to instrument settings has yet to be established and, additionally, the effect of variability inherent in authentic fire debris (e.g., water content) has not yet been explored. In this work, we quantitatively evaluate the effect of 11 factors via a sensitivity analysis with simulated fire debris. The factors studied included six controllable instrument settings and five reflecting debris characteristics. We quantified performance by covariance mapping between gas chromatography – mass spectrometry (GC–MS) retention time – ion abundance matrices for the recovered eluates and corresponding reference samples. Six factors were found to be significant. IL volume, IL weathering, and debris quantity significantly affected the recovered eluates, whereas water content did not. As related to recovering IL residue from simulated fire debris, recommended instrument settings include a higher oven temperature, longer equilibration time, larger volume of extracted headspace (collection volume), and a lower inlet flow rate. Together with the covariance mapping metric, the fractional factorial design successfully addressed questions about the effect of instrument factors, debris factors, and their interactions with an efficient number of experiments.
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