Uncertainty analysis of microwave electronic measurements enables the quantification of device performance and aides in the development of robust technology. The Monte Carlo method is commonly used ...to attain accurate uncertainty analyses for complicated nonlinear systems. Combining multiple similar measurements, each with a Monte Carlo uncertainty analysis, allows one to incorporate the uncertainty given by their spread. In this paper, we compare two Monte Carlo sampling methods, illustrate that one method reduces the bias of averaged quantities, show how this impacts computed uncertainties, and highlight microwave applications for which this corrected method can be applied.
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 two different disease transmission models. First, we develop a Bayesian estimation procedure that 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 implement a particle Markov chain Monte Carlo algorithm to approximate the posterior distribution of the hidden SIRS model parameters. We test this method using both simulated data and data from Mathbaria, Bangladesh. We use the posterior distribution of the hidden SIRS model parameters 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 apply this Bayesian analysis to data from multiple geographical areas in Bangladesh to test the generalizability of our methods and results. We then expand our analysis of the Mathbaria data to include multiple environmental covariates shifted in time by multiple lags, testing estimation and prediction in the presence of multiple highly correlated predictors. Finally, we add an additional latent water compartment to the hidden SIRS model and explore the difficulties of parameter estimation and cholera outbreak prediction using this complex, but biologically more realistic model for cholera transmission.
Background 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. Methodology/Principal Findings 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. Conclusions 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.
We quantify random uncertainties for scattering-parameters repeatedly measured with a vector network analyzer, focusing on variations due to multiple calibrations, disconnects, and repeat ...measurements. We describe a two-stage nested design, which allows us to model the random effects, and present results for a series of coaxial measurements performed by making use of an open-short-load-thru calibration kit with Type-N connectors.
We investigate the effects of IF (intermediate-frequency) bandwidth and averaging on calibrated scattering-parameter measurements made with a vector network analyzer. We begin by examining the sweep ...times and noise-floor levels for various combinations of the two settings. Then, we study how these settings influence calibrated measurements and compare the results to uncertainties due to systematic and random effects for devices with varying insertion-loss values.
We verified the performance of a correlation-based channel sounder in the 3550 MHz to 3650 MHz band with a calibrated vector network analyzer (VNA) by comparing measurements in a stable, coaxial ...environment at the same reference planes. The purpose of this experiment was to focus on the performance of the channel sounder's hardware, as opposed to antenna effects or channel variations. Two conducted propagation channels were utilized - one consisting of a length of cable and an attenuator to simulate a line-of-sight channel, and another with a pair of splitters joined by cables of different lengths to simulate a multipath environment. Performing repeated measurements and estimating the components of uncertainty due to random effects, we found that the channel sounder and VNA measurements agreed to within 0.25 dB for values of path gain, and the peaks in the power delay profile agreed to within 2 dB.
Uncertainty propagation software can have unknown, inadvertent biases introduced by various means. This work is a case study in bias identification and reduction in one such software package, the ...Microwave Uncertainty Framework (MUF). The general purpose of the MUF is to provide automated multivariate statistical uncertainty propagation and analysis on a Monte Carlo (MC) basis. Combine is a key module in the MUF, responsible for merging data, raw or transformed, to accurately reflect the variability in the data and in its central tendency. In this work the performance of Combine's MC replicates is analytically compared against its stated design goals. An alternative construction is proposed for Combine's MC replicates and its performance is compared, too, against Combine's design goals. These comparisons are made within an archetypal two-stage scenario in which received data are first transformed in conjunction with shared systematic error and then combined to produce summary information. These comparisons reveal the limited conditions under which Combine's uncertainty results are unbiased and the extent of these biases when these conditions are not met. For small MC sample sizes neither construction, current or alternative, fully meets Combine's design goals, nor does either construction consistently outperform the other. However, for large MC sample sizes the bias in the proposed alternative construction is asymptotically zero, and this construction is recommended.
Laser power metrology at the National Institute of Standards and Technology (NIST) ranges 20 orders of magnitude from photon-counting (1000 photons/s) to 100 kW (10^23 photons/s at a wavelength of ...1070 nm). As a part of routine practices, we perform internal (unpublished) comparisons between our various power meters to verify correct operation.
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 non-stationary, 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 \(6\times10^{-19}\), showing that O-TWTFT can support free-space atomic clock comparisons below the \(10^{-18}\) level.
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