395 research outputs found

    Statistical analysis of time-resolved emission from ensembles of semiconductor quantum dots: Interpretation of exponential decay models

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    We present a statistical analysis of time-resolved spontaneous emission decay curves from ensembles of emitters, such as semiconductor quantum dots, with the aim of interpreting ubiquitous non-single-exponential decay. Contrary to what is widely assumed, the density of excited emitters and the intensity in an emission decay curve are not proportional, but the density is a time integral of the intensity. The integral relation is crucial to correctly interpret non-single-exponential decay. We derive the proper normalization for both a discrete and a continuous distribution of rates, where every decay component is multiplied by its radiative decay rate. A central result of our paper is the derivation of the emission decay curve when both radiative and nonradiative decays are independently distributed. In this case, the well-known emission quantum efficiency can no longer be expressed by a single number, but is also distributed. We derive a practical description of non-single-exponential emission decay curves in terms of a single distribution of decay rates; the resulting distribution is identified as the distribution of total decay rates weighted with the radiative rates. We apply our analysis to recent examples of colloidal quantum dot emission in suspensions and in photonic crystals, and we find that this important class of emitters is well described by a log-normal distribution of decay rates with a narrow and a broad distribution, respectively. Finally, we briefly discuss the Kohlrausch stretched-exponential model, and find that its normalization is ill defined for emitters with a realistic quantum efficiency of less than 100%.\ud \u

    Assignment of the evidential value of a fingermark general pattern using a Bayesian network

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    Abstract: When visible on a fingermark, the general pattern maintains its importance in the fingerprint examination procedure, since the difference between the general pattern of a fingermark and a fingerprint is sufficient for exclusion. In the current work, the importance of the general pattern is extended by evaluating the strength of evidence of a match given corresponding general pattern. In current practice (due to the lack of statistical support for the general pattern evidence) the fingerprint examiners assign personal probabilities to the general pattern evidence based on their knowledge and experience, while in this work the probabilities are calculated using a Bayesian Network which is fed by empirical data. 1

    A sustainability charge on meat

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    This study, commissioned by the True Animal Protein Price Coalition (TAPP Coalition), sets out a proposal for a policy package to incentivize the farming sector to reduce its environmental footprint and encourage consumers to adopt a more sustainable diet. Without appropriate financial policies, in the form of taxes or subsidies, the earnings model of sustainable agriculture and livestock farming is constrained. It is desirable, furthermore, that the policy package is equitable and does not lead to a disproportionately high financial burden for lower-income households. The study reflects two of the core premises the Dutch government has set for the Climate Agreement:1.Use of cost-effective policy instruments, and2.Equitable allocation of costs and benefits.In the ‘EU summary’, we present a rough, exploratory analysis of introducing a meat sustainability charge on a European scale. In this 2-pager, the indicative European results are summarized and elaborated on with an indication of effects on meat consumption in Europe in 2030

    A sustainability charge on meat

    Get PDF
    This study, commissioned by the True Animal Protein Price Coalition (TAPP Coalition), sets out a proposal for a policy package to incentivize the farming sector to reduce its environmental footprint and encourage consumers to adopt a more sustainable diet. Without appropriate financial policies, in the form of taxes or subsidies, the earnings model of sustainable agriculture and livestock farming is constrained. It is desirable, furthermore, that the policy package is equitable and does not lead to a disproportionately high financial burden for lower-income households. The study reflects two of the core premises the Dutch government has set for the Climate Agreement:1.Use of cost-effective policy instruments, and2.Equitable allocation of costs and benefits.In the ‘EU summary’, we present a rough, exploratory analysis of introducing a meat sustainability charge on a European scale. In this 2-pager, the indicative European results are summarized and elaborated on with an indication of effects on meat consumption in Europe in 2030

    Evaluating the strength of evidence of elemental profiling of polymers with LA-ICP-MS

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    LA-ICP-MS is a powerful technique for obtaining a forensic elemental profile of polymer evidence materials. However, the lack of homogeneous polymer reference standards hampers database creation and reliably matching a sample to a specific source. Therefore, the current study aims to evaluate the strength of evidence of forensic polymer comparisons by applying a matrix-matched reference standard with known concentrations for elements of interest. Four datasets of tapes, electrical wires, tubing, and jerrycans were compiled using LA-ICP-MS. It was found that quantification with the new PVC standard or by simply using the response of one element as internal standard significantly reduced the between-run variation. For each class of polymeric materials, characteristic elements could be identified with PCA and LDA. To facilitate classification, elemental concentrations were found to be typical for specific colors and types of polymeric materials. For forensic comparison, a score-based Bayesian likelihood ratio model and the t-test overlap method performed better than the feature-based model and 4-sigma criterion, in terms of rates of misleading evidence. Normalization to 13C and quantification with the PVC standard with and without prior normalization to 13C slightly reduced rates of misleading evidence. The t-test method showed an overall average false inclusion rate of only 0.45% and a false exclusion rate of 2.4%. Maximum calibrated likelihood ratios of 0.014 to 1778 were found for the tape dataset. In conclusion, this study demonstrates that with the use of proper standards, quantitative elemental profiling with LA-ICP-MS is a promising tool for forensic classification and comparison of polymers
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