62 research outputs found
Ethane in Titan's Stratosphere from Cassini CIRS Far- and Mid-Infrared Spectra
The Cassini Composite Infrared Spectrometer (CIRS) observed thermal emission in the far- and mid-infrared (from 10 to 1500 cm(exp 1)), enabling spatiotemporal studies of ethane on Titan across the span of the Cassini mission from 2004 through 2017. Many previous measurements of ethane on Titan have relied on modeling the molecules mid-infrared (sub 12) band, centered on 822 cm(exp 1). Other bands of ethane at shorter and longer wavelengths were seen, but have not been modeled to measure ethane abundance. Spectral line lists of the far-infrared (sub 4) torsional band at 289 cm(exp 1) and the mid-infrared (sub 8) band centered at 1468 cm(exp 1) have recently been studied in the laboratory. We model CIRS observations of each of these bands (along with the (sub 12) band) separately and compare the retrieved mixing ratios from each spectral region. Nadir observations of the (sub 4) band probe the low stratosphere below 100 km. Our equatorial measurements at 289 cm(exp 1) show an abundance of (1.00.4)x10(exp 5) at 88 km from 2007 to 2017. This mixing ratio is consistent with measurements at higher altitudes, in contrast to the depletion that many photochemical models predict. Measurements from the (sub 12) and (sub 8) bands are comparable to each other, with the (sub 12) band probing an altitude range that extends deeper in the atmosphere. We suggest that future studies of planetary atmospheres may observe the (sub 8) band, enabling shorter wavelength studies of ethane. There may also be an advantage to observing both the ethane (sub 8) band and nearby methane (sub 4) band in the same spectral window
Ethane in Titan's Stratosphere from Cassini CIRS Far- And Mid-infrared Spectra
The Cassini Composite Infrared Spectrometer (CIRS) observed thermal emission
in the far- and mid-infrared (from 10 cm to 1500 cm), enabling
spatiotemporal studies of ethane on Titan across the span of the Cassini
mission from 2004 through 2017. Many previous measurements of ethane on Titan
have relied on modeling the molecule's mid-infrared band, centered
on 822 cm. Other bands of ethane at shorter and longer wavelengths were
seen, but have not been modeled to measure ethane abundance. Spectral line
lists of the far-infrared torsional band at 289 cm and the
mid-infrared band centered ay 1468 cm have recently been
studied in the laboratory. We model CIRS observations of each of these bands
(along with the band) separately and compare retrieved mixing ratios
from each spectral region. Nadir observations of of the band probe
the low stratosphere below 100 km. Our equatorial measurements at 289 cm
show an abundance of (1.00.4) 10 at 88 km, from 2007 to
2017. This mixing ratio is consistent with measurements at higher altitudes, in
contrast to the depletion that many photochemical models predict. Measurements
from the and bands are comparable to each other, with the
band probing an altitude range that extends deeper in the
atmosphere. We suggest future studies of planetary atmospheres may observe the
band, enabling shorter wavelength studies of ethane. There may also
be an advantage to observing both the ethane band and nearby methane
band in the same spectral window.Comment: 19 pages, 10 figure
Vacuum Energy Density Fluctuations in Minkowski and Casimir States via Smeared Quantum Fields and Point Separation
We present calculations of the variance of fluctuations and of the mean of
the energy momentum tensor of a massless scalar field for the Minkowski and
Casimir vacua as a function of an intrinsic scale defined by a smeared field or
by point separation. We point out that contrary to prior claims, the ratio of
variance to mean-squared being of the order unity is not necessarily a good
criterion for measuring the invalidity of semiclassical gravity. For the
Casimir topology we obtain expressions for the variance to mean-squared ratio
as a function of the intrinsic scale (defined by a smeared field) compared to
the extrinsic scale (defined by the separation of the plates, or the
periodicity of space). Our results make it possible to identify the spatial
extent where negative energy density prevails which could be useful for
studying quantum field effects in worm holes and baby universe, and for
examining the design feasibility of real-life `time-machines'.
For the Minkowski vacuum we find that the ratio of the variance to the
mean-squared, calculated from the coincidence limit, is identical to the value
of the Casimir case at the same limit for spatial point separation while
identical to the value of a hot flat space result with a temporal
point-separation. We analyze the origin of divergences in the fluctuations of
the energy density and discuss choices in formulating a procedure for their
removal, thus raising new questions into the uniqueness and even the very
meaning of regularization of the energy momentum tensor for quantum fields in
curved or even flat spacetimes when spacetime is viewed as having an extended
structure.Comment: 41 pages, 2 figure
Noise Kernel and Stress Energy Bi-Tensor of Quantum Fields in Hot Flat Space and Gaussian Approximation in the Optical Schwarzschild Metric
Continuing our investigation of the regularization of the noise kernel in
curved spacetimes [N. G. Phillips and B. L. Hu, Phys. Rev. D {\bf 63}, 104001
(2001)] we adopt the modified point separation scheme for the class of optical
spacetimes using the Gaussian approximation for the Green functions a la
Bekenstein-Parker-Page. In the first example we derive the regularized noise
kernel for a thermal field in flat space. It is useful for black hole
nucleation considerations. In the second example of an optical Schwarzschild
spacetime we obtain a finite expression for the noise kernel at the horizon and
recover the hot flat space result at infinity. Knowledge of the noise kernel is
essential for studying issues related to black hole horizon fluctuations and
Hawking radiation backreaction. We show that the Gaussian approximated Green
function which works surprisingly well for the stress tensor at the
Schwarzschild horizon produces significant error in the noise kernel there. We
identify the failure as occurring at the fourth covariant derivative order.Comment: 21 pages, RevTeX
Rapid detection of pandemic influenza in the presence of seasonal influenza
Background: Key to the control of pandemic influenza are surveillance systems that raise alarms rapidly and sensitively. In addition, they must minimise false alarms during a normal influenza season. We develop a method that uses historical syndromic influenza data from the existing surveillance system 'SERVIS' (Scottish Enhanced Respiratory Virus Infection Surveillance) for influenza-like illness (ILI) in Scotland. Methods: We develop an algorithm based on the weekly case ratio (WCR) of reported ILI cases to generate an alarm for pandemic influenza. From the seasonal influenza data from 13 Scottish health boards, we estimate the joint probability distribution of the country-level WCR and the number of health boards showing synchronous increases in reported influenza cases over the previous week. Pandemic cases are sampled with various case reporting rates from simulated pandemic influenza infections and overlaid with seasonal SERVIS data from 2001 to 2007. Using this combined time series we test our method for speed of detection, sensitivity and specificity. Also, the 2008-09 SERVIS ILI cases are used for testing detection performances of the three methods with a real pandemic data. Results: We compare our method, based on our simulation study, to the moving-average Cumulative Sums (Mov-Avg Cusum) and ILI rate threshold methods and find it to be more sensitive and rapid. For 1% case reporting and detection specificity of 95%, our method is 100% sensitive and has median detection time (MDT) of 4 weeks while the Mov-Avg Cusum and ILI rate threshold methods are, respectively, 97% and 100% sensitive with MDT of 5 weeks. At 99% specificity, our method remains 100% sensitive with MDT of 5 weeks. Although the threshold method maintains its sensitivity of 100% with MDT of 5 weeks, sensitivity of Mov-Avg Cusum declines to 92% with increased MDT of 6 weeks. For a two-fold decrease in the case reporting rate (0.5%) and 99% specificity, the WCR and threshold methods, respectively, have MDT of 5 and 6 weeks with both having sensitivity close to 100% while the Mov-Avg Cusum method can only manage sensitivity of 77% with MDT of 6 weeks. However, the WCR and Mov-Avg Cusum methods outperform the ILI threshold method by 1 week in retrospective detection of the 2009 pandemic in Scotland. Conclusions: While computationally and statistically simple to implement, the WCR algorithm is capable of raising alarms, rapidly and sensitively, for influenza pandemics against a background of seasonal influenza. Although the algorithm was developed using the SERVIS data, it has the capacity to be used at other geographic scales and for different disease systems where buying some early extra time is critical
Spatio-temporal patterns of malaria infection in Bhutan: a country embarking on malaria elimination
<p>Abstract</p> <p>Background</p> <p>At the verge of elimination of malaria in Bhutan, this study was carried out to analyse the trend of malaria in the endemic districts of Bhutan and to identify malaria clusters at the sub-districts. The findings would aid in implementing the control activities. Poisson regression was performed to study the trend of malaria incidences at district level from 1994 to 2008. Spatial Empirical Bayesian smoothing was deployed to identify clusters of malaria at the sub-district level from 2004 to 2008.</p> <p>Results</p> <p>Trend of the overall districts and most of the endemic districts have decreased except Pemagatshel, which has an increase in the trend. Spatial cluster-outlier analysis showed that malaria clusters were mostly concentrated in the central and eastern Bhutan in three districts of Dagana, Samdrup Jongkhar and Sarpang. The disease clusters were reported throughout the year. Clusters extended to the non-transmission areas in the eastern Bhutan.</p> <p>Conclusions</p> <p>There is significant decrease in the trend of malaria with the elimination at the sight. The decrease in the trend can be attributed to the success of the control and preventive measures. In order to realize the target of elimination of malaria, the control measure needs to be prioritized in these high-risk clusters of malaria.</p
Human pluripotent stem cell models of autism spectrum disorder: emerging frontiers, opportunities, and challenges towards neuronal networks in a dish
Federated learning enables big data for rare cancer boundary detection.
Although machine learning (ML) has shown promise across disciplines, out-of-sample generalizability is concerning. This is currently addressed by sharing multi-site data, but such centralization is challenging/infeasible to scale due to various limitations. Federated ML (FL) provides an alternative paradigm for accurate and generalizable ML, by only sharing numerical model updates. Here we present the largest FL study to-date, involving data from 71 sites across 6 continents, to generate an automatic tumor boundary detector for the rare disease of glioblastoma, reporting the largest such dataset in the literature (n = 6, 314). We demonstrate a 33% delineation improvement for the surgically targetable tumor, and 23% for the complete tumor extent, over a publicly trained model. We anticipate our study to: 1) enable more healthcare studies informed by large diverse data, ensuring meaningful results for rare diseases and underrepresented populations, 2) facilitate further analyses for glioblastoma by releasing our consensus model, and 3) demonstrate the FL effectiveness at such scale and task-complexity as a paradigm shift for multi-site collaborations, alleviating the need for data-sharing
Author Correction: Federated learning enables big data for rare cancer boundary detection.
10.1038/s41467-023-36188-7NATURE COMMUNICATIONS14
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