Conditional linearizability criteria for a system of third-order ordinary differential equations

We provide linearizability criteria for a class of systems of third-order ordinary differential equations (ODEs) that is cubically semi-linear in the first derivative, by differentiating a system of second-order quadratically semi-linear ODEs and using the original system to replace the second derivative. The procedure developed splits into two cases, those where the coefficients are constant and those where they are variables. Both cases are discussed and examples given

Self-referenced continuous-variable quantum key distribution protocol

We introduce a new continuous-variable quantum key distribution (CV-QKD) protocol, self-referenced CV-QKD, that eliminates the need for transmission of a high-power local oscillator between the communicating parties. In this protocol, each signal pulse is accompanied by a reference pulse (or a pair of twin reference pulses), used to align Alice's and Bob's measurement bases. The method of phase estimation and compensation based on the reference pulse measurement can be viewed as a quantum analog of intradyne detection used in classical coherent communication, which extracts the phase information from the modulated signal. We present a proof-of-principle, fiber-based experimental demonstration of the protocol and quantify the expected secret key rates by expressing them in terms of experimental parameters. Our analysis of the secret key rate fully takes into account the inherent uncertainty associated with the quantum nature of the reference pulse(s) and quantifies the limit at which the theoretical key rate approaches that of the respective conventional protocol that requires local oscillator transmission. The self-referenced protocol greatly simplifies the hardware required for CV-QKD, especially for potential integrated photonics implementations of transmitters and receivers, with minimum sacrifice of performance. As such, it provides a pathway towards scalable integrated CV-QKD transceivers, a vital step towards large-scale QKD networks.Comment: 14 pages, 10 figures. Published versio

Current carrying capacity of carbon nanotubes

The current carrying capacity of ballistic electrons in carbon nanotubes that are coupled to ideal contacts is analyzed. At small applied voltages, where electrons are injected only into crossing subbands, the differential conductance is $4e^2/h$. At applied voltages larger than $\Delta E_{NC}/2e$ ($\Delta E_{NC}$ is the energy level spacing of first non crossing subbands), electrons are injected into non crossing subbands. The contribution of these electrons to current is determined by the competing processes of Bragg reflection and Zener type inter subband tunneling. In small diameter nanotubes, Bragg reflection dominates, and the maximum differential conductance is comparable to $4e^2/h$. Inter subband Zener tunneling can be non negligible as the nanotube diameter increases because $\Delta E_{NC}$ is inversely proportional to the diameter. As a result, with increasing nanotube diameter, the differential conductance becomes larger than $4e^2/h$, though not comparable to the large number of subbands into which electrons are injected from the contacts. These results may be relevant to recent experiments in large diameter multi-wall nanotubes that observed conductances larger than $4e^2/h$.Comment: 12 pages, 4 figure

Development and Validation of the Computational Thinking Concepts and Skills Test

Calls for standardized and validated measures of computational thinking have been made repeatedly in recent years. Still, few such tests have been created and even fewer have undergone rig- orous psychometric evaluation and been made available to re- searchers. The purpose of this study is to report our work in de- veloping and validating a test of computational thinking concepts and skills and to compare different scoring methods for the test. This computational thinking exam is intended to be used in com- puting education research as a common measure of computational thinking so that the research community will be able to make more meaningful comparisons across samples and studies. The Computational Thinking Concepts and Skills Test (CTCAST) was administered to students in several courses, evaluated and revised, and then administered to another group of students. Part of the revision included changing half of the items to a multiple-select format. The test scores using the three scoring methods were com- pared to each other and to scores on a different test of core com- puter science knowledge. Results indicate the CTCAST and the test of core computer science knowledge measure similar, but not identical, aspects of students’ knowledge and skills, and that item- level statistics vary according to the scoring method that is used. Recommendations for using and scoring the test are presented

Development and Validation of the Computational Thinking Concepts and Skills Test

Calls for standardized and validated measures of computational thinking have been made repeatedly in recent years. Still, few such tests have been created and even fewer have undergone rig- orous psychometric evaluation and been made available to re- searchers. The purpose of this study is to report our work in de- veloping and validating a test of computational thinking concepts and skills and to compare different scoring methods for the test. This computational thinking exam is intended to be used in com- puting education research as a common measure of computational thinking so that the research community will be able to make more meaningful comparisons across samples and studies. The Computational Thinking Concepts and Skills Test (CTCAST) was administered to students in several courses, evaluated and revised, and then administered to another group of students. Part of the revision included changing half of the items to a multiple-select format. The test scores using the three scoring methods were com- pared to each other and to scores on a different test of core com- puter science knowledge. Results indicate the CTCAST and the test of core computer science knowledge measure similar, but not identical, aspects of students’ knowledge and skills, and that item- level statistics vary according to the scoring method that is used. Recommendations for using and scoring the test are presented

Development and Validation of the Computational Thinking Concepts and Skills Test

Calls for standardized and validated measures of computational thinking have been made repeatedly in recent years. Still, few such tests have been created and even fewer have undergone rig- orous psychometric evaluation and been made available to re- searchers. The purpose of this study is to report our work in de- veloping and validating a test of computational thinking concepts and skills and to compare different scoring methods for the test. This computational thinking exam is intended to be used in com- puting education research as a common measure of computational thinking so that the research community will be able to make more meaningful comparisons across samples and studies. The Computational Thinking Concepts and Skills Test (CTCAST) was administered to students in several courses, evaluated and revised, and then administered to another group of students. Part of the revision included changing half of the items to a multiple-select format. The test scores using the three scoring methods were com- pared to each other and to scores on a different test of core com- puter science knowledge. Results indicate the CTCAST and the test of core computer science knowledge measure similar, but not identical, aspects of students’ knowledge and skills, and that item- level statistics vary according to the scoring method that is used. Recommendations for using and scoring the test are presented

The mosaic of surface charge in contact electrification

When dielectric materials are brought into contact and then separated, they develop static electricity. For centuries, it has been assumed that such contact charging derives from the spatially homogeneous material properties (along the material's surface) and that within a given pair of materials, one charges uniformly positively and the other negatively. We demonstrate that this picture of contact charging is incorrect. Whereas each contact-electrified piece develops a net charge of either positive or negative polarity, each surface supports a random "mosaic" of oppositely charged regions of nanoscopic dimensions. These mosaics of surface charge have the same topological characteristics for different types of electrified dielectrics and accommodate significantly more charge per unit area than previously thought

Stripe formation in high-Tc superconductors

The non-uniform ground state of the two-dimensional three-band Hubbard model for the oxide high-Tc superconductors is investigated using a variational Monte Carlo method. We examine the effect produced by holes doped into the antiferromagnetic (AF) background in the underdoped region. It is shown that the AF state with spin modulations and stripes is stabilized du to holes travelling in the CuO plane. The structures of the modulated AF spins are dependent upon the parameters used in the model. The effect of the boundary conditions is reduced for larger systems. We show that there is a region where incommensurability is proportional to the hole density. Our results give a consistent description of stripes observed by the neutron- scattering experiments based on the three-band model for CuO plane.Comment: 8 pages, 9 figure

Selectively tunable optical Stark effect of anisotropic excitons in atomically thin ReS2

The optical Stark effect is a coherent light-matter interaction describing the modification of quantum states by non-resonant light illumination in atoms, solids and nanostructures. Researchers have strived to utilize this effect to control exciton states, aiming to realize ultra-high-speed optical switches and modulators. However, most studies have focused on the optical Stark effect of only the lowest exciton state due to lack of energy selectivity, resulting in low degree-of-freedom devices. Here, by applying a linearly polarized laser pulse to few-layer ReS2, where reduced symmetry leads to strong in-plane anisotropy of excitons, we control the optical Stark shift of two energetically separated exciton states. Especially, we selectively tune the Stark effect of an individual state with varying light polarization. This is possible because each state has a completely distinct dependence on light polarization due to different excitonic transition dipole moments. Our finding provides a methodology for energy-selective control of exciton states.111612Ysciescopu