RKKY Interactions in Graphene Landau Levels

We study RKKY interactions for magnetic impurities on graphene in situations where the electronic spectrum is in the form of Landau levels. Two such situations are considered: non-uniformly strained graphene, and graphene in a real magnetic field. RKKY interactions are enhanced by the lowest Landau level, which is shown to form electron states binding with the spin impurities and add a strong non-perturbative contribution to pairwise impurity spin interactions when their separation $R$ no more than the magnetic length. Beyond this interactions are found to fall off as $1/R^3$ due to perturbative effects of the negative energy Landau levels. Based on these results, we develop simple mean-field theories for both systems, taking into account the fact that typically the density of states in the lowest Landau level is much smaller than the density of spin impurities. For the strain field case, we find that the system is formally ferrimagnetic, but with very small net moment due to the relatively low density of impurities binding electrons. The transition temperature is nevertheless enhanced by them. For real fields, the system forms a canted antiferromagnet if the field is not so strong as to pin the impurity spins along the field. The possibility that the system in this latter case supports a Kosterlitz-Thouless transition is discussed

Survey on Controlable Image Synthesis with Deep Learning

Image synthesis has attracted emerging research interests in academic and industry communities. Deep learning technologies especially the generative models greatly inspired controllable image synthesis approaches and applications, which aim to generate particular visual contents with latent prompts. In order to further investigate low-level controllable image synthesis problem which is crucial for fine image rendering and editing tasks, we present a survey of some recent works on 3D controllable image synthesis using deep learning. We first introduce the datasets and evaluation indicators for 3D controllable image synthesis. Then, we review the state-of-the-art research for geometrically controllable image synthesis in two aspects: 1) Viewpoint/pose-controllable image synthesis; 2) Structure/shape-controllable image synthesis. Furthermore, the photometrically controllable image synthesis approaches are also reviewed for 3D re-lighting researches. While the emphasis is on 3D controllable image synthesis algorithms, the related applications, products and resources are also briefly summarized for practitioners.Comment: 19 pages, 17 figure

Unusual Electronic Transport and Magnetism in Titanium Oxide based Semiconductors and Metals

The main objective of this thesis was to explore the structural, electrical, magnetic and optical properties of titanium based novel oxide thin films, such as transparent conducting oxides (TCOs) and diluted magnetic semiconductors (DMSs), so as to be able to realize optoelectronics and spintronics applications. I demonstrated that niobium doped titanium dioxide (TiO2) in its epitaxial anatase phase grown at certain condition is an intrinsic transparent conducting oxide, with both its conductivity and transparency comparable to that of the commercial transparent electrode In-Sn-O being widely used in current optoelectronic devices. I investigated the growth parameter dependence of structure and conductivity of this material. It was found that the growth temperature is a crucial parameter for the structural quality as well as the electron mobility, while the oxygen partial pressure is essential for the conduction electron concentration. The excellent conductivity of niobium doped TiO2 should be attributed to the extremely high solubility of niobium in the TiO2 matrix as well as a very shallow donor level created in the TiO2 band gap. I investigated several important oxide based DMS systems, such as niobium and cobalt dual doped TiO2, transition metal (TM) element doped SrTiO3 etc. I found that niobium dual doping is an effective way to introduce carriers into the classical Co: TiO2 system, which provides the feasibility of studying the RKKY interaction in this system by chemical doping. Our detailed characterization of TM doped SrTiO3 questioned the intrinsic nature of the ferromagnetism observed by other groups. By a systematic study of Hall effect on superparamagnetic Co-(La,Sr)TiO3 thin films, I was able to demonstrate that the magnitude of the anomalous Hall effect is a way to distinguish between intrinsic and extrinsic DMS. A Kondo effect was observed in niobium doped TiO2 grown at certain condition. The origin of magnetic moments in this system was suggested to be from the cation vacancy defects. This observation of defect magnetism in conventional non-magnetic TiO2 may shed light on the occurrence of ferromagnetism in oxide diluted magnetic semiconductors

Analysis of a high-pier railway bridge under spatial stochastic stationary and non-stationary earthquake excitations

Ciljevi ovoga rada su provesti komparativnu analizu velikog sustava željezničkog mosta na visokim stupovima izloženog stacionarnim i ne-stacionarnim prostorno promjenjivim uzbudama potresa primjenom metode pseudo-uzbude (pseudo-excitation method - PEM), te procijeniti može li se ili ne može ne-stacionarna stohastička analiza željezničkih mostova na visokim stupovima izloženih trosmjernim prostornim podzemnim gibanjima zamijeniti jednostavnijom stacionarnom slučajnom analizom kako bi se izbjegla prekomjerna računanja. Zasnovane na ANSYS softveru konačnih elemenata, analize stacionarnih i ne-stacionarnih stohastičkih uzbuda mosta na visokim stupovima pretvorile su se u harmonične analize i determinističke prijelazne analize u našem istraživanju, primjenom PEM-a. Učinak prolaza vala i učinak nekoherentnosti modelirani su kao ključni čimbenici, a ukupno je razmotreno dvanaest slučajeva u svrhu ispitivanja učinka prolaza vala i učinka nekoherentnosti na seizmičku reakciju željezničkog mosta na visokim stupovima izloženog stacionarnim i ne-stacionarnim uzbudana potresa. Rezultati pokazuju da je reakcija konstrukcije pod stacionarnom uzbudom veća nego kod ne-stacionarne uzimajući u obzir bilo učinak prolaza vala ili učinak nekoherencije. Kad se uspoređuju reakcije konstrukcije pod stacionarnom pobudom s onima kod ne-stacionarne, sve stope rasta su manje od 25 %, što je u tehnici prihvatljivo, a to znači da se ne-stacionarna stohastička analiza željezničkih mostova na visokim stupovima pri trosmjernim prostornim gibanjima u zemlji može pojednostavniti u stacionarnu analizu kako bi se izbjeglo prekomjerno računanje.The objectives of this paper are to perform a comparative analysis of the large-scale system of a high-pier railway bridge subjected to stationary and non-stationary spatially varying earthquake excitations using the pseudo-excitation method (PEM), and to estimate whether or not the non-stationary stochastic analysis of the high-pier railway bridges under tri-directional spatial ground motions can be simplified into a stationary random analysis to avoid excessive computation. Based on the finite element software ANSYS, the stationary and non-stationary stochastic excitations analyses of a high-pier bridge were transformed into harmonic analyses and deterministic transient analyses in the study, respectively, by using PEM. The wave-passage effect and the incoherence effect were modelled as the key factors, a total of twelve cases were considered to investigate the wave-passage effect and incoherence effect on the seismic response of a high-pier railway bridge under stationary and non-stationary earthquake excitations. Results show that structural responses under stationary excitation are larger than those under non-stationary by considering either the wave-passage effect or the incoherence effect. Through comparing structural responses under stationary excitation with those under non-stationary one, all the growth rates are less than 25 %, which is acceptable in engineering, meaning that a non-stationary stochastic analysis of high-pier railway bridges under tri-directional spatial ground motions can be simplified into a stationary analysis to avoid excessive computation

Design for Postplacement Mousing based on GSM in Long-Distance

This design for mousing is made up of power control module, infrared sensor module, signal processing module, distance information transportation based on GSM and device of power grid. The design consists of two sets of conductors, separately linked by fire wire and null line and distributing alternatively. The major innovation is infrared sensor module with Fresnel lens, and that the infrared detecting area should be spread in one direction at least. When the mouse get into the infrared detecting area, the sensor signal of infrared detecting device is sent to power control module through signal element and then starts the device of power grid to power up to make the mouse be shocked or die. GSM module is adopted to tell that the mouse is caught successfully. This design can be placed in any position that the mouse is always out and no need of baits

Muscle activity-driven green-oriented random number generation mechanism to secure WBSN wearable device communications

Wireless body sensor networks (WBSNs) mostly consist of low-cost sensor nodes and implanted devices which generally have extremely limited capability of computations and energy capabilities. Hence, traditional security protocols and privacy enhancing technologies are not applicable to the WBSNs since their computations and cryptographic primitives are normally exceedingly complicated. Nowadays, mobile wearable and wireless muscle-computer interfaces have been integrated with the WBSN sensors for various applications such as rehabilitation, sports, entertainment, and healthcare. In this paper, we propose MGRNG, a novel muscle activity-driven green-oriented random number generation mechanism which uses the human muscle activity as green energy resource to generate random numbers (RNs). The RNs can be used to enhance the privacy of wearable device communications and secure WBSNs for rehabilitation purposes. The method was tested on 10 healthy subjects as well as 5 amputee subjects with 105 segments of simultaneously recorded surface electromyography signals from their forearm muscles. The proposed MGRNG requires only one second to generate a 128-bit RN, which is much more efficient when compared to the electrocardiography-based RN generation algorithms. Experimental results show that the RNs generated from human muscle activity signals can pass the entropy test and the NIST random test and thus can be used to secure the WBSN nodes

Nanotube spin defects for omnidirectional magnetic field sensing

Optically addressable spin defects in three-dimensional (3D) crystals and two-dimensional (2D) van der Waals (vdW) materials are revolutionizing nanoscale quantum sensing. Spin defects in one-dimensional (1D) vdW nanotubes will provide unique opportunities due to their small sizes in two dimensions and absence of dangling bonds on side walls. However, optically detected magnetic resonance of localized spin defects in a nanotube has not been observed. Here, we report the observation of single spin color centers in boron nitride nanotubes (BNNTs) at room temperature. Our findings suggest that these BNNT spin defects possess a spin $S=1/2$ ground state without an intrinsic quantization axis, leading to orientation-independent magnetic field sensing. We harness this unique feature to observe anisotropic magnetization of a 2D magnet in magnetic fields along orthogonal directions, a challenge for conventional spin $S=1$ defects such as diamond nitrogen-vacancy centers. Additionally, we develop a method to deterministically transfer a BNNT onto a cantilever and use it to demonstrate scanning probe magnetometry. Further refinement of our approach will enable atomic scale quantum sensing of magnetic fields in any direction.Comment: 9 pages, 5 figure