University of Nebraska–Lincoln

About: University of Nebraska–Lincoln is a education organization based out in Lincoln, Nebraska, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 28059 authors who have published 61544 publications receiving 2139104 citations. The organization is also known as: Nebraska & UNL.

The theory and practice of item response theory.

Abstract: Symbols and Acronyms Part 1 Introduction to Measurement Measurement Some Measurement Issues Item Response Theory Classical Test Theory Latent Class Analysis Summary Part 2 The One-Parameter Model Conceptual Development of the Rasch Model The One-Parameter Model The One-Parameter Logistic Model and the Rasch Model Assumptions underlying the Model An Empirical Data Set: The Mathematics Data Set Conceptually Estimating an Individual's Location Some Pragmatic Characteristics of Maximum Likelihood Estimates The Standard Error of Estimate and Information An Instrument's Estimation Capacity Summary Part 3 Joint Maximum Likelihood Parameter Estimation Joint Maximum Likelihood Estimation Indeterminacy of Parameter Estimates How Large a Calibration Sample? Example: Application of the Rasch Model to the Mathematics Data, JMLE Summary Part 4 Marginal Maximum Likelihood Parameter Estimation Marginal Maximum Likelihood Estimation Estimating an Individual's Location: Expected A Posteriori Example: Application of the Rasch Model to the Mathematics Data, MMLE Metric Transformation and the Total Characteristic Function Summary Part 5 The Two-Parameter Model Conceptual Development of the Two-Parameter Model Information for the Two-Parameter Model Conceptual Parameter Estimation for the 2PL Model How Large a Calibration Sample? Metric Transformation, 2PL Model Example: Application of the 2PL Model to the Mathematics Data, MMLE Information and Relative Efficiency Summary Part 6 The Three-Parameter Model Conceptual Development of the Three-Parameter Model Additional Comments about the Pseudo-Guessing Parameter Conceptual Estimation for the 3PL Model How Large a Calibration Sample? Assessing Conditional Independence Example: Application of the 3PL Model to the Mathematics Data, MMLE Assessing Person Fit: Appropriateness Measurement Information for the Three-Parameter Model Metric Transformation, 3PL Model Handling Missing Responses Issues to Consider in Selecting among the 1PL, 2PL, and 3PL Models Summary Part 7 Rasch Models for Ordered Polytomous Data Conceptual Development of the Partial Credit Model Conceptual Parameter Estimation of the PC Model Example: Application of the PC Model to a Reasoning Ability Instrument, MMLE The Rating Scale Model Conceptual Estimation of the RS Model Example: Application of the RS Model to an Attitudes toward Condom Scale, JMLE How Large a Calibration Sample? Information for the PC and RS Models Metric Transformation, PC and RS Models Summary Part 8 Non-Rasch Models for Ordered Polytomous Data The Generalized Partial Credit Model Example: Application of the GPC Model to a Reasoning Ability Instrument, MMLE Conceptual Development of the Graded Response Model How Large a Calibration Sample? Example: Application of the GR Model to an Attitudes toward Condom Scale, MMLE Information for Graded Data Metric Transformation, GPC and GR Models Summary Part 9 Models for Nominal Polytomous Data Conceptual Development of the Nominal Response Model How Large a Calibration Sample? Example: Application of the NR Model to a Science Test, MMLE Example: Mixed Model Calibration of the Science Test-NR and PC Models, MMLE Example: NR and PC Mixed Model Calibration of the Science Test, Collapsed Options, MMLE Information for the NR Model Metric Transformation, NR Model Conceptual Development of the Multiple-Choice Model Example: Application of the MC Model to a Science Test, MMLE Example: Application of the BS Model to a Science Test, MMLE Summary Part 10 Models for Multidimensional Data Conceptual Development of a Multidimensional IRT Model Multidimensional Item Location and Discrimination Item Vectors and Vector Graphs The Multidimensional Three-Parameter Logistic Model Assumptions of the MIRT Model Estimation of the M2PL Model Information for the M2PL Model Indeterminacy in MIRT Metric Transformation, M2PL Model Example: Application of the M2PL Model, Normal-Ogive Harmonic Analysis Robust Method Obtaining Person Location Estimates Summary Part 11 Linking and Equating Equating Defined Equating: Data Collection Phase Equating: Transformation Phase Example: Application of the Total Characteristic Function Equating Summary Part 12 Differential Item Functioning Differential Item Functioning and Item Bias Mantel-Haenszel Chi-Square The TSW Likelihood Ratio Test Logistic Regression Example: DIF Analysis Summary Appendix A: Maximum Likelihood Estimation of Person Locations Estimating an Individual's Location: Empirical Maximum Likelihood Estimation Estimating an Individual's Location: Newton's Method for MLE Revisiting Zero Variance Binary Response Patterns Appendix B: Maximum Likelihood Estimation of Item Locations Appendix C: The Normal Ogive Models Conceptual Development of the Normal Ogive Model The Relationship between IRT Statistics and Traditional Item Analysis Indices Relationship of the Two-Parameter Normal Ogive and Logistic Models Extending the Two-Parameter Normal Ogive Model to a Multidimensional Space Appendix D: Computerized Adaptive Testing A Brief History Fixed-Branching Techniques Variable-Branching Techniques Advantages of Variable-Branching over Fixed-Branching Methods IRT-Based Variable-Branching Adaptive Testing Algorithm Appendix E Miscellanea Linear Logistic Test Model (LLTM) Using Principal Axis for Estimating Item Discrimination Infinite Item Discrimination Parameter Estimates Example: NOHARM Unidimensional Calibration An Approximate Chi-Square Statistic for NOHARM Mixture Models Relative Efficiency, Monotonicity, and Information FORTRAN Formats Example: Mixed Model Calibration of the Science Test-NR and 2PL Models, MMLE Example: Mixed Model Calibration of the Science Test-NR and GR Models, MMLE Odds, Odds Ratios, and Logits The Person Response Function Linking: A Temperature Analogy Example Should DIF Analyses Be Based on Latent Classes? The Separation and Reliability Indices Dependency in Traditional Item Statistics and Observed Scores

Non-wetting surface-driven high-aspect-ratio crystalline grain growth for efficient hybrid perovskite solar cells

Abstract: Large-aspect-ratio grains are needed in polycrystalline thin-film solar cells for reduced charge recombination at grain boundaries; however, the grain size in organolead trihalide perovskite (OTP) films is generally limited by the film thickness. Here we report the growth of OTP grains with high average aspect ratio of 2.3-7.9 on a wide range of non-wetting hole transport layers (HTLs), which increase nucleus spacing by suppressing heterogeneous nucleation and facilitate grain boundary migration in grain growth by imposing less drag force. The reduced grain boundary area and improved crystallinity dramatically reduce the charge recombination in OTP thin films to the level in OTP single crystals. Combining the high work function of several HTLs, a high stabilized device efficiency of 18.3% in low-temperature-processed planar-heterojunction OTP devices under 1 sun illumination is achieved. This simple method in enhancing OTP morphology paves the way for its application in other optoelectronic devices for enhanced performance.

Ion Migration in Organometal Trihalide Perovskite and Its Impact on Photovoltaic Efficiency and Stability

Abstract: ConspectusOrganometal trihalide perovskites (OTPs) are emerging as very promising photovoltaic materials because the power conversion efficiency (PCE) of OTP solar cells quickly rises and now rivals with that of single crystal silicon solar cells after only five-years research. Their prospects to replace silicon photovoltaics to reduce the cost of renewable clean energy are boosted by the low-temperature solution processing as well as the very low-cost raw materials and relative insensitivity to defects. The flexibility, semitransparency, and vivid colors of perovskite solar cells are attractive for niche applications such as built-in photovoltaics and portable lightweight chargers. However, the low stability of current hybrid perovskite solar cells remains a serious issue to be solved before their broad application. Among all those factors that affect the stability of perovskite solar cells, ion migration in OTPs may be intrinsic and cannot be taken away by device encapsulation.The presence of ion migrat...