3,567 research outputs found
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 . At applied voltages larger than
( 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 . Inter subband Zener tunneling can be non negligible as
the nanotube diameter increases because is inversely
proportional to the diameter. As a result, with increasing nanotube diameter,
the differential conductance becomes larger than , 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 .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
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