Fixing the c Parameter in the Three-Parameter Logistic Model

For several decades, the three-parameter logistic model (3PLM) has been the dominant choice for practitioners in the field of educational measurement for modeling examinee\u27s response data from multiple-choice (MC) items. Past studies, however, have pointed out that the c-parameter of 3PLM should not be interpreted as a guessing parameter. This study found logical, empirical evidence showing that neither the a-, b-, or c-parameters of 3PLM can accurately reflect the discrimination, difficulty, and guessing properties of an item, respectively. This study reconceptualized the problem-solving and guessing processes with a modification of the 3PLM that eliminates ambiguity in modeling the guessing process. A series of studies using various real and simulated data demonstrated that the suggested model, in which the c-parameters were fixed at a computed probability for successful random guessing (i.e., c = 1 / k with k being the number of options), could provide a more feasible, stable, and accurate item estimation solution without sacrificing the model fit compared with a typical 3PLM. Accessed 13,077 times on https://pareonline.net from January 09, 2012 to December 31, 2019. For downloads from January 1, 2020 forward, please click on the PlumX Metrics link to the right

Symmetry Breaking Phase Transitions in ABJM Theory with a Finite U(1) Chemical Potential

We consider the U(1) charged sector of ABJM theory at finite temperature, which corresponds to the Reissner-Nordstrom AdS black hole in the dual type IIA supergravity description. Including back-reaction to the bulk geometry, we show that phase transitions occur to a broken phase where SU(4) R-symmetry of the field theory is broken spontaneously by the condensation of dimension one or two operators. We show both numerically and analytically that the relevant critical exponents for the dimension one operator agree precisely with those of mean field theory in the strongly coupled regime of the large N planar limit.Comment: 22 pages, 6 figures, typos corrected, references added, improved figures, minor changes, accepted for publication in Phys. Rev.

Impact of Violation of the Missing-at-Random Assumption on Full-Information Maximum Likelihood Method in Multidimensional Adaptive Testing

The full-information maximum likelihood (FIML) method makes it possible to estimate and analyze structural equation models (SEM) even when data are partially missing, enabling incomplete data to contribute to model estimation. The cornerstone of FIML is the missing-at-random (MAR) assumption. In (unidimensional) computerized adaptive testing (CAT), unselected items (i.e., responses that are not observed) remain at random even though selected items (i.e., responses that are observed) have been associated with a test taker’s latent trait that is being measured. In multidimensional adaptive testing (MAT), however, the missingness in the response data partially depends on the unobserved data because items are selected based on various types of information including the covariance among latent traits. This eventually may lead to violations of MAR. This study aimed to evaluate the potential impact such a violation of MAR in MAT could have on FIML estimation performance. The results showed an increase in estimation errors in item parameter estimation when the MAT response data were used, and differences in the level of the impact depending on how items loaded on multiple latent traits. Accessed 4,728 times on https://pareonline.net from May 19, 2014 to December 31, 2019. For downloads from January 1, 2020 forward, please click on the PlumX Metrics link to the right

Induced local spin-singlet amplitude and pseudogap in high TcT_{c} cuprates

In this paper we show that local spin-singlet amplitude with d-wave symmetry, , can be induced by short-range spin correlations even in the absence of pairing interactions. Fluctuation theory is formulated to make connection between pseudogap temperature $T^{*}$, pseudogap size $\Delta_{pg}$ and . In the present scenario for the pseudogap, the normal state pseudogap is caused by the induced local spin-singlet amplitude due to short-range spin correlations, which compete in the low energy sector with superconducting correlations to make $T_{c}$ go to zero near half-filling. Calculated $T^{*}$ falls from a high value onto the $T_{c}$ line and closely follows mean-field N\'{e}el temperature $T_{N}^{MF}$. The calculated $\Delta_{pg}$ is in good agreement with experimental results. We propose an experiment in which the present scenario can be critically tested.Comment: 5 pages, 3 figure

Homotopy Structure of 5d Vacua

It is shown that flat zero-energy solutions (vacua) of the 5d Kaluza-Klein theory admit a non-trivial homotopy structure generated by certain Kaluza-Klein excitations. These vacua consist of an infinite set of homotopically different spacetimes denoted by $\mathcal{M}^{(n)}_5$, among which $\mathcal{M}^{(0)}_5$ and $\mathcal{M}^{(1)}_5$ are especially identified as $M_{4} \times S^{1}$ and $M_5$, the ground states of the 5d Kaluza-Klein theory and the 5d general relativity, respectively (where $M_k$ represents the $k$-dimensional Minkowski space).Comment: 8 page

Characteristics of oxygen isotope substitutions in the quasiparticle spectrum of Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta}

There is an ongoing debate about the nature of the bosonic excitations responsible for the quasiparticle self energy in high temperature superconductors -- are they phonons or spin fluctuations? We present a careful analysis of the bosonic excitations as revealed by the `kink' feature at 70 meV in angle resolved photoemission data using Eliashberg theory for a d-wave superconductor. Starting from the assumption that nodal quasiparticles are not coupled to the $(\pi,\pi)$ magnetic resonance, the sharp structure at $70$meV can be assigned to phonons. We find that not only can we account for the shifts of the kink energy seen on oxygen isotope substitution but also get a quantitative estimate of the fraction of the area under the electron-boson spectral density which is due to phonons. We conclude that for optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ phonons contribute $\sim 10$% and non-phononic excitations $\sim 90$%.Comment: 6 pages, 3 figure

Conditions for magnetically induced singlet d-wave superconductivity on the square lattice

It is expected that at weak to intermediate coupling, d-wave superconductivity can be induced by antiferromagnetic fluctuations. However, one needs to clarify the role of Fermi surface topology, density of states, pseudogap, and wave vector of the magnetic fluctuations on the nature and strength of the induced d-wave state. To this end, we study the generalized phase diagram of the two-dimensional half-filled Hubbard model as a function of interaction strength $U/t$, frustration induced by second-order hopping $t^{\prime}/t$, and temperature $T/t$. In experiment, $U/t$ and $t^{\prime}/t$ can be controlled by pressure. We use the two-particle self-consistent approach (TPSC), valid from weak to intermediate coupling. We first calculate as a function of $t^{\prime}/t$ and $U/t$ the temperature and wave vector at which the spin response function begins to grow exponentially.D-wave superconductivity in a half-filled band can be induced by such magnetic fluctuations at weak to intermediate coupling, but only if they are near commensurate wave vectors and not too close to perfect nesting conditions where the pseudogap becomes detrimental to superconductivity. For given $U/t$ there is thus an optimal value of frustration $t^{\prime}/t$ where the superconducting $T_c$ is maximum. The non-interacting density of states plays little role. The symmetry d$_{x^{2}-y^{2}}$ vs d$_{xy}$ of the superconducting order parameter depends on the wave vector of the underlying magnetic fluctuations in a way that can be understood qualitatively from simple arguments

Using Hierarchical Data Mining to Characterize Performance of Wireless System Configurations

This paper presents a statistical framework for assessing wireless systems performance using hierarchical data mining techniques. We consider WCDMA (wideband code division multiple access) systems with two-branch STTD (space time transmit diversity) and 1/2 rate convolutional coding (forward error correction codes). Monte Carlo simulation estimates the bit error probability (BEP) of the system across a wide range of signal-to-noise ratios (SNRs). A performance database of simulation runs is collected over a targeted space of system configurations. This database is then mined to obtain regions of the configuration space that exhibit acceptable average performance. The shape of the mined regions illustrates the joint influence of configuration parameters on system performance. The role of data mining in this application is to provide explainable and statistically valid design conclusions. The research issue is to define statistically meaningful aggregation of data in a manner that permits efficient and effective data mining algorithms. We achieve a good compromise between these goals and help establish the applicability of data mining for characterizing wireless systems performance

Miro, MCU, and calcium: Bridging our understanding of mitochondrial movement in axons

Neurons are extremely polarized structures with long axons and dendrites, which require proper distribution of mitochondria and maintenance of mitochondrial dynamics for neuronal functions and survival. Indeed, recent studies show that various neurological disorders are linked to mitochondrial transport in neurons. Mitochondrial anterograde transport is believed to deliver metabolic energy to synaptic terminals where energy demands are high, while mitochondrial retrograde transport is required to repair or remove damaged mitochondria in axons. It has been suggested that Ca2+ plays a key role in regulating mitochondrial transport by altering the configuration of mitochondrial protein, miro. However, molecular mechanisms that regulate mitochondrial transport in neurons still are not well characterized. In this review, we will discuss the roles of miro in mitochondrial transport and how the recently identified components of the mitochondrial calcium uniporter add to our current model of mitochondrial mobility regulation.open2