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The interpretation of neutron cross section experiments depends upon an in-depth knowledge of the physical characteristics of the target sample. An x-ray image of an encapsulated metallic Eu sample used in a neutron cross section ...
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The interpretation of neutron cross section experiments depends upon an in-depth knowledge of the physical characteristics of the target sample. An x-ray image of an encapsulated metallic Eu sample used in a neutron cross section measurement showed a very non-uniform thickness as well as holes in the sample. In light of this problem it was found necessary to determine the thickness distribution in four thin metallic Eu samples without disturbing the encapsulation (and exposing the Eu to air). All four Eu samples were subsequently x-rayed along with a Sm step wedge. The gray levels in the Eu images were then compared to the Sm gray levels and, taking into account differences in the x-ray absorption and density of Eu and Sm, the sample thickness distributions were obtained for each Eu sample. This work demonstrates that a step wedge can be used to calibrate x-ray images to a thickness scale, and allows the thickness variation of the samples to be represented in a simple probability table for incorporation into the analysis of neutron experiments.
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Understanding HIV incidence, the rate at which new infections occur in populations, is critical for tracking and surveillance of the epidemic. In this article, we derive methods for determining sample sizes for cross-sectional sur...
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Understanding HIV incidence, the rate at which new infections occur in populations, is critical for tracking and surveillance of the epidemic. In this article, we derive methods for determining sample sizes for cross-sectional surveys to estimate incidence with sufficient precision. We further show how to specify sample sizes for two successive cross-sectional surveys to detect changes in incidence with adequate power. In these surveys biomarkers such as CD4 cell count, viral load, and recently developed serological assays are used to determine which individuals are in an early disease stage of infection. The total number of individuals in this stage, divided by the number of people who are uninfected, is used to approximate the incidence rate. Our methods account for uncertainty in the durations of time spent in the biomarker defined early disease stage. We find that failure to account for this uncertainty when designing surveys can lead to imprecise estimates of incidence and underpowered studies. We evaluated our sample size methods in simulations and found that they performed well in a variety of underlying epidemics. Code for implementing our methods in R is available with this article at the Biometrics website on Wiley Online Library.
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Clinical studies using complex sampling often involve both truncation and censoring, where there are options for the assumptions of independence of censoring and event and for the relationship between censoring and truncation. In ...
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Clinical studies using complex sampling often involve both truncation and censoring, where there are options for the assumptions of independence of censoring and event and for the relationship between censoring and truncation. In this paper, we clarify these choices, show certain equivalences, and provide examples.
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The shock wave generates the strain gradient and consequent electric polarization in samples due to the flexoelectric effect during the impact process. At present, some scholars have studied the influence law of different impact v...
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The shock wave generates the strain gradient and consequent electric polarization in samples due to the flexoelectric effect during the impact process. At present, some scholars have studied the influence law of different impact velocities, but the influence of different thickness and cross-sectional area of samples on flexoelectric effect is still blank. In this letter, we have studied the voltage variation of barium titanate samples with different thickness and cross-sectional area under a certain impact velocity. The results show that the maximum voltage value caused by flexoelectric effect increases as the thickness increases, which is basically in positive proportion; it decreases with the increase of diameter, which is in inverse proportion. This research will lay a theoretical foundation for the fabrication of flexoelectricity sensor.
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In this paper we consider the problem of estimating a conditional distribution function in a nonparametric way, when the response variable is nonnegative, and the observational procedure is length-biased. We propose a proper adapt...
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In this paper we consider the problem of estimating a conditional distribution function in a nonparametric way, when the response variable is nonnegative, and the observational procedure is length-biased. We propose a proper adaptation of the estimate to right-censoring provoked by limitation in following-up. Large sample analysis of the introduced estimator is given, including rates of convergence, limiting distribution, and efficiency results. We show that the length-bias model results in less variance in estimation, when compared to methods based on observed truncation times. Practical performance of the proposed estimator is explored through simulations. Application to unemployment data analysis is provided.
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Cross sections are frequently used in the stratigraphic study of pictorial structures. Thanks to cross sections, it is possible to study and record original and non-original strata that may provide important information regarding ...
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Cross sections are frequently used in the stratigraphic study of pictorial structures. Thanks to cross sections, it is possible to study and record original and non-original strata that may provide important information regarding the artist's technique and later restoration processes. This information helps conservators design different strategies in processes such as cleaning. However, it is often in cleaning where the advantages and limitations of cross sections become obvious. When dealing with a complex structure, cross sections may not be enough to record in a comprehensive and accurate manner all the strata removed during cleaning. In some cases, the conservator may obtain during cleaning a great amount of stratigraphic information that is not visible in the cross sections. Therefore, it may be necessary to resort to other recording systems, such as the stratigraphic unit recording sheet and the stratigraphic diagram, which are frequently used in archaeological stratigraphy. This article demonstrates how cross-section analysis was combined with stratigraphic study during the cleaning of two panel paintings to gain an improved understanding of their complicated layer structure.
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Observation of lifetimes by means of cross-sectional surveys typically results in left-truncated, right-censored data. In some applications, it may be assumed that the truncation variable is uniformly distributed on some time inte...
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Observation of lifetimes by means of cross-sectional surveys typically results in left-truncated, right-censored data. In some applications, it may be assumed that the truncation variable is uniformly distributed on some time interval, leading to the so-called length-biased sampling. This information is relevant, since it allows for more efficient estimation of survival and related parameters. In this work we introduce and analyze new empirical methods in the referred scenario, when the sampled lifetimes are at risk of Type I censoring from the right. We illustrate the method with real economic data.
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Statistical models for time-to-pregnancy data are usually formulated in discrete time. Two approaches were surveyed, including methods of accounting for both known heterogeneity (covariates, possibly time-dependent) and unknown he...
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Statistical models for time-to-pregnancy data are usually formulated in discrete time. Two approaches were surveyed, including methods of accounting for both known heterogeneity (covariates, possibly time-dependent) and unknown heterogeneity (frailty). Delicate censoring and truncation patterns arose for prospective and, particu- larly, retrospective sampling designs. The inclusion of several pregnancies per couple presents new challenges and possibilities.
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Focus ion beam preparation of transmission electron microscopy (TEM) samples has become increasingly popular due to the relative ease of extraction of TEM foils from specific locations within a larger sample. However the sputterin...
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Focus ion beam preparation of transmission electron microscopy (TEM) samples has become increasingly popular due to the relative ease of extraction of TEM foils from specific locations within a larger sample. However the sputtering damage induced by Ga ion bombardment in focus ion beam means that traditional electropolishing may be a preferable method. First, we describe a special electropolishing method for the preparation of irregular TEM samples from ex-service nuclear reactor components, spring-shaped spacers. This method has also been used to prepare samples from a nonirradiated component for a TEM in situ heavy ion irradiation study. Because the specimen size is small (0.7 × 0.7 × 3 mm), a sandwich installation is adopted to obtain high quality polishing. Second, we describe some modifications to a conventional TEM cross-section sample preparation method that employs Ni electroplating. There are limitations to this method when preparing cross-section samples from either (1) metals which are difficult to activate for electroplating, or (2) a heavy ion irradiated foil with a very shallow damage layer close to the surface, which may be affected by the electroplating process. As a consequence, a novel technique for preparing cross-section samples was developed and is described.
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