1,348 research outputs found

    A numerical study of two-photon ionization of helium using the Pyprop framework

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    Few-photon induced breakup of helium is studied using a newly developed ab initio numerical framework for solving the six-dimensional time-dependent Schroedinger equation. We present details of the method and calculate (generalized) cross sections for the process of two-photon nonsequential (direct) double ionization at photon energies ranging from 39.4 to 54.4 eV, a process that has been very much debated in recent years and is not yet fully understood. In particular, we have studied the convergence property of the total cross section in the vicinity of the upper threshold (54.4 eV), versus the pulse duration of the applied laser field. We find that the cross section exhibits an increasing trend near the threshold, as has also been observed by others, and show that this rise cannot solely be attributed to an unintended inclusion of the sequential two-photon double ionization process, caused by the bandwidth of the applied field.Comment: 7 pages, 3 figure

    First principle-based Research on properties of twisted bilayer of Graphene and GaN

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    Since quantum theory was founded in 1920s, it has developed quite rapidly and led people to a new field that totally different from the classical ones. As the size of an object decrease to a certain level, the classical physical law would be invalid and quantum mechanics would become the ruler of object behaviors. The property under quantum mechanics achieves functions that never been seen before. So, scientist would invent new materials and devices with properties that never found before. This is the reason that new materials and devices have been emerging due to vast developments in nanotechnologies. The project of my PHD research in four years is to research and analysis the property of nano semiconductor materials. In this thesis, there are mainly four parts. The first part is Introduction. In this part the basic concepts and related information would be listed. The second part is the first project that guide me to the further study. This project is set to simulate the electronic transport in quantum region based on the Schrodinger equation for random shaped energy barriers, which is very basic to quantum mechanics. The method of simulation is matlab coding. The simulation will help in understanding the concept of quantum field and applications in design and analysis of nanometer scale devices and systems. The third part is my first paper. In this paper I cooperate with my workmate Shuo Deng and we investigate the electron transport and thermoelectric property of twisted bilayer graphene nanoribbon junction (TBGNRJ) in 0o, 21.8o, 38.2o and 60o rotation angles by first principles calculation with Landauer-Buttiker and Boltzmann theories. It is found that TBGNRJs exhibit a strong reduction of thermal conductance compared with the single graphene nanoribbon (GNR) and negative differential resistance (NDR) in 21.8 o and 38.2 o rotation angles under ±0.2 V bias voltage. More importantly, three peak ZT values of 2.0, 2.7 and 6.1 can be achieved in the 21.8o rotation angle at 300K. The outstanding ZT values of TBGNRJs are interpreted as the combination of the reduced thermal conductivity and enhanced electrical conductivity at optimized angles. The fourth part is my second paper. In this paper I report electronic and optical properties of the GaN bilayer structures that are rotated in plane at several optimized rotation angles by using the density functional theory method. For the aim of maintaining the structural stability and using a small cell size, the twisting angles of the GaN bilayer structures are optimized to be 27.8°, 38.2° and 46.8° using the crystal matching theory. The last part is conclusion, possible further study and acknowledgement

    Improved recursive Green's function formalism for quasi one-dimensional systems with realistic defects

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    We derive an improved version of the recursive Green's function formalism (RGF), which is a standard tool in the quantum transport theory. We consider the case of disordered quasi one-dimensional materials where the disorder is applied in form of randomly distributed realistic defects, leading to partly periodic Hamiltonian matrices. The algorithm accelerates the common RGF in the recursive decimation scheme, using the iteration steps of the renormalization decimation algorithm. This leads to a smaller effective system, which is treated using the common forward iteration scheme. The computational complexity scales linearly with the number of defects, instead of linearly with the total system length for the conventional approach. We show that the scaling of the calculation time of the Green's function depends on the defect density of a random test system. Furthermore, we discuss the calculation time and the memory requirement of the whole transport formalism applied to defective carbon nanotubes

    Parameterization of AR231453: A Potent Agonist of the GPR119 Receptor, a Target for Diabetes Treatment

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    The first reported potent agonist for the GPR119 receptor, a potential target for the treatment of diabetes, is 2-fluoro-4-methanesulfonyl-phenyl-{6-[4-(3-isopropyl-[1,2,4]oxadiazol-5-yl)-piperidin-1-yl]-5-nitro-pyrimidin-4-yl}-amine (AR231453). The dynamic interactions of AR231453 with GPR119 using molecular dynamics simulation are of great interest. However, parameters for AR231453 that describe the behavior of the molecule in the CHARMM force field have not been determined. The following study produces parameters by creating model fragments and compares the produced parameters to quantum calculations. The produced parameters are then further refined within the Visual Molecular Dynamics (VMD) program’s plugin program, the Force Field Toolkit as well as Gaussian 09 and CHARMM. Molecular dynamics simulations are done to study the orientation of AR231453 in a lipid bilayer

    Quantum Algorithm of Imperfect KB Self-organization Pt I: Smart Control-Information-Thermodynamic Bounds

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    The quantum self-organization algorithm model of wise knowledge base design for intelligent fuzzy controllers with required robust level considered. Background of the model is a new model of quantum inference based on quantum genetic algorithm. Quantum genetic algorithm applied on line for the quantum correlation’s type searching between unknown solutions in quantum superposition of imperfect knowledge bases of intelligent controllers designed on soft computing. Disturbance conditions of analytical information-thermodynamic trade-off interrelations between main control quality measures (as new design laws) discussed in Part I. The smart control design with guaranteed achievement of these tradeoff interrelations is main goal for quantum self-organization algorithm of imperfect KB. Sophisticated synergetic quantum information effect in Part I (autonomous robot in unpredicted control situations) and II (swarm robots with imperfect KB exchanging between “master - slaves”) introduced: a new robust smart controller on line designed from responses on unpredicted control situations of any imperfect KB applying quantum hidden information extracted from quantum correlation. Within the toolkit of classical intelligent control, the achievement of the similar synergetic information effect is impossible. Benchmarks of intelligent cognitive robotic control applications considered

    DESIGN OF GRAPHENE-BASED SENSORS FOR NUCLEIC ACIDS DETECTION AND ANALYSIS

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    DNA (Deoxyribonucleic Acid) is the blueprint of life as it encodes all genetic information. In genetic disorder such as gene fusion, Copy Number Variation (CNV), and single nucleotide polymorphism, Nucleic acids such as DNA bases detection and analysis is used as the gold standard for successful diagnosis. Researchers have been conducting rigorous studies to achieve genome sequences at low cost while maintaining high accuracy and high throughput. A quick, accurate, and low-cost DNA detection approach would revolutionize medicine. Genome sequence helps to enhance people’s perception of inheritance, disease, and individuality. This research aims to improve DNA bases detection accuracy, and efficiency, and reduce the production cost, thus novel based sensors were developed to detect and identify the DNA bases. This work aims at first to develop specialized field effect transistors which will acquire real-time detection for different concentrations of DNA. The sensor was developed with a channel of graphite oxide between gold electrodes on a substrate of a silicon wafer using Quantumwise Atomistix Toolkit (ATK) and its graphical user interfaces Virtual Nanolab (VNL). The channel was decorated with trimetallic nanoclusters that include gold, silver, and platinum which have high affinity to DNA. The developed sensor was investigated by both simulation and experiment. The second aim of this research was to analyze the tissue transcriptome through DNA bases detection, thus novel graphene-based sensors with a nanopore were designed and developed to detect the different DNA nucleobases (Adenine (A), Cytosine (C), Guanine (G), Thymine (T)). This research focuses on the simulation of charge transport properties for the developed sensors. This work includes experimental fabrication and software simulation studies of the electronic properties and structural characteristics of the developed sensors. Novel sensors were modeled using Quantumwise Atomistix Toolkit (ATK) and its graphical user Interface Virtual Nanolab (VNL) where several electronic properties were studied including transmission spectrum and electrical current of DNA bases inside the sensor’s nanopore. The simulation study resulted in a unique current for each of the DNA bases within the nanopore. This work suggests that the developed sensors could achieve DNA sequencing with high accuracy. The practical implementation of this work represents the ability to predict and cure diseases from the genetic makeup perspective

    Electronic transport in metallic carbon nanotubes with mixed defects within the strong localization regime

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    We study the electron transport in metallic carbon nanotubes (CNTs) with realistic defects of different types. We focus on large CNTs with many defects in the mesoscopic range. In a recent paper we demonstrated that the electronic transport in those defective CNTs is in the regime of strong localization. We verify by quantum transport simulations that the localization length of CNTs with defects of mixed types can be related to the localization lengths of CNTs with identical defects by taking the weighted harmonic average. Secondly, we show how to use this result to estimate the conductance of arbitrary defective CNTs, avoiding time consuming transport calculations
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