Interacting topological magnons in a checkerboard ferromagnet

This work is devoted to studying the magnon-magnon interaction effect in a two-dimensional checkerboard ferromagnet with the Dzyaloshinskii-Moriya interaction.Using a first-order Green function method,we analyze the influence of magnon-magnon interaction on the magnon band topology.We find that Chern numbers of two renormalized magnon bands are different above and below the critical temperature,which means that the magnon band gap-closing phenomenon is an indicator for one topological phase transition of the checkerboard ferromagnet.Our results show that the checkerboard ferromagnet possesses two topological phases,and its topological phase can be controlled either via the temperature or the applied magnetic field due to magnon-magnon interactions.Interestingly,it is found that the topological phase transition can occur twice with the increase in the temperature,which is different from the results of the honeycomb ferromagnet.

R^n上的基于Checkerboard格点的不可分双正交小波

研究了一类基于Checkerboard格点的不可分双正交小波,并证明了其尺度函数逼近阶与光滑性的上界.在此基础上提出了此类小波的构造算法.理论分析表明,使用该算法构造的小波具有很好的对称性、光滑性以及对多维信号采样的视觉优势.此外该算法能够构造具有任意给定消失矩的小波,并且其小波滤波器具有有理系数,这在多维信号处理中具有重要意义.实例分析也验证了构造算法的有效性和上述结论.

Checkerboard法对ε-聚赖氨酸和壳聚糖抑菌作用的研究

该研究以大肠杆菌和金黄色葡萄球菌为指示菌,探究ε-聚赖氨酸和壳聚糖复配溶液的抑菌效果。结果表明:6μg/mLε-聚赖氨酸和100μg/mL壳聚糖复配溶液对大肠杆菌的抑制作用最佳;16μg/mLε-聚赖氨酸和100μg/mL壳聚糖复配溶液对金黄色葡萄球菌的抑制作用最佳。Checkerboard法表明壳聚糖和ε-聚赖氨酸抑菌作用具有叠加效应。ε-聚赖氨酸与壳聚糖复配溶液处理能够使细菌出现蛋白质泄漏现象。

Automatic three-dimensional reconstruction based on four-view stereo vision using checkerboard pattern

An automatic three-dimensional(3D) reconstruction method based on four-view stereo vision using checkerboard pattern is presented. Mismatches easily exist in traditional binocular stereo matching due to the repeatable or similar features of binocular images. In order to reduce the probability of mismatching and improve the measure precision, a four-camera measurement system which can add extra matching constraints and offer multiple measurements is applied in this work. Moreover, a series of different checkerboard patterns are projected onto the object to obtain dense feature points and remove mismatched points. Finally, the 3D model is generated by performing Delaunay triangulation and texture mapping on the point cloud obtained by four-view matching. This method was tested on the 3D reconstruction of a terracotta soldier sculpture and the Buddhas in the Mogao Grottoes. Their point clouds without mismatched points were obtained and less processing time was consumed in most cases relative to binocular matching. These good reconstructed models show the effectiveness of the method.

STUDY ON PARAMETERS FOR TOPOLOGICAL VARIABLES FIELD INTERPOLATED BY MOVING LEAST SQUARE APPROXIMATION

This paper presents a new approach to the structural topology optimization of continuum structures. Material-point independent variables are presented to illustrate the existence condition,or inexistence of the material points and their vicinity instead of elements or nodes in popular topology optimization methods. Topological variables field is constructed by moving least square approximation which is used as a shape function in the meshless method. Combined with finite element analyses,not only checkerboard patterns and mesh-dependence phenomena are overcome by this continuous and smooth topological variables field,but also the locations and numbers of topological variables can be arbitrary. Parameters including the number of quadrature points,scaling parameter,weight function and so on upon optimum topological configurations are discussed. Two classic topology optimization problems are solved successfully by the proposed method. The method is found robust and no numerical instabilities are found with proper parameters.

The ICM method with objective function transformed by variable discrete condition for continuum structure

ICM （Independent Continuous Mapping） method can solve topological optimization problems with the minimized weight as the objective and subjected to displacement constraints. To get a clearer topological configuration, by introducing the discrete condition of topological variables and integrating with the original objective, an optimal model with multi-objectives is formulated to make the topological variables approach 0 or 1 as near as possible, and the model reduces the effect of deleting rate on the result. The image-filtering method is employed to eliminate the checkerboard patterns and mesh dependence that occurred in the topology optimization of a continuum structure. The computational efficiency is enhanced through selecting quasi-active displacement constraints and a design region. Numerical examples indicate that this algorithm is robust and practicable, though the number of iterations is slightly increased with respect to the original algorithm.

A new technique for high precision sub-regional camera calibration based on checkerboard pattern

Camera calibration is critical in computer vision measurement system, affecting the accuracy of the whole system. Many camera calibration methods have been proposed, but they cannot consider precision and operation complexity at the same time. In this paper, a new technique is proposed to calibrate camera. Firstly, the global calibration method is described in de-tail. It requires the camera to observe a checkerboard pattern shown at a few different orientations. The checkerboard corners are obtained by Harris algorithm. With direct linear transformation and non-linear optimal algorithm, the global calibration pa-rameters are obtained. Then, a sub-regional method is proposed. Those corners are divided into two groups, middle corners and edge corners, which are used to calibrate the corresponding area to get two sets of calibration parameters. Finally, some experimental images are used to test the proposed method. Experimental results demonstrate that the average projection error of sub-region method is decreased at least 16% compared with the global calibration method. The proposed technique is simple and accurate. It is suitable for the industrial computer vision measurement.

Sand-fixing characteristics of Carex brunnescens and its application with straw checkerboard technique in restoration of degraded alpine meadows

Carex brunnescens（Pers.）, a typical clonal species, is considered to be the only herb found to date that can develop on sand dunes in Maqu alpine region of northwestern China. However, the characteristics that C. brunnescens resists to harsh alpine environment have not been documented. In this study, we conducted a field investigation to determine the morphological, reproductive, and sand-fixing characteristics of C. brunnescens. Concomitantly, we transplanted the belowground rhizomes of C. brunnescens to sand dunes and compared the abilities to restore degraded alpine meadows among sand dunes that had no further treatment（SD＋N）, sand dunes that had straw checkerboard technique but no transplanted rhizomes of C. brunnescens（SD＋SCT）, and sand dunes that had both SCT and transplanted rhizomes of C. brunnescens（SD＋SCT＋P）. We found that belowground vertical rhizomes and horizontal rhizomes（including branching rhizomes and main rhizomes） of C. brunnescens were highly developed and that population reproduction was dominated by horizontal rhizomes. C. brunnescens exhibited a significant sand-fixation effect under following conditions： population density was 145–156 ramets/m^2, vegetation cover was 31.2%–39.3%, total length of belowground rhizomes was 11,223 cm/m^2, total length of belowground first-order roots was 9161–10,524 cm/m^2, fresh weight of aboveground part was 198.5–212.6 g/m^2, and fresh weight of belowground part was 578.8–612.4 g/m^2. It should be particularly noted that SD＋SCT＋P treatment（sand dunes that had both straw checkerboard technique and transplanted rhizomes of C. brunnescens） was the best and SD＋N（sand dunes that had no further treatment） was the worst in terms of following biotic indicators： total number of reproductive ramets, total number of belowground rhizomes, and fresh weight of aboveground and belowground parts of C. brunnescens, contents of soil organic carbon, available nitrogen, microbial biomass carbon, and microbial biomass nitrogen. It implies that applying SCT in sand dunes and transplanting belowground rhizomes to sand dunes with SCT could improve both soil fertility and growth of C. brunnescens. These results suggest that the SCT-promoted high reproductive abilities of belowground rhizomes of C. brunnescens can successfully facilitate the establishment of ramets and can thus be an effective strategy to restore degraded vegetation in Maqu alpine region of northwestern China.

Sand control effect of HDPE sandbreak nets with different porosity structure

Straw checkerboard sand barriers with a porous structure that consists of a pervious upper portion and a dense lower portion are widely used to achieve great sand control effect.Considering this,and resolving the serious earth surface undercutting problem after HDPE sandbreak net checkboard barriers setting,the authors used HDPE(high-density polyethylene)materials to prepare new sandbreak materials with a similar porous structure.Through wind tunnel simulations and field sand control monitoring,we compared the sand control effect of three HDPE sandbreak nets with different porosity structure.Compared to the sandbreak net with uniform porosity structure,the three types of HDPE sandbreak nets with different porosity structure had poorer effect on reducing sand transport rates,but had longer effective protection distance before sandbreak nets at low wind velocity conditions(<12 m/s),longer effective protection distance at high wind velocity(>14 m/s)and longer effective protection distance between sandbreak nets at all experimental wind velocity conditions.Wind and sand control effect characteristics of HDPE sandbreak nets with different porosity structure provide an ideal material on semiburied checkerboard sand barriers for sand stabilization.By contrast,uniform-type sandbreak nets are used as materials on high upright sand fences for sand blocking.These HDPE sandbreak nets can be used to replace traditional sandbreak materials and have a very high potential for widespread and popular application in aeolian sand disaster control.

Hubbard model on an anisotropic checkerboard lattice at finite temperatures: Magnetic and metal–insulator transitions

We study magnetic and Mott transitions of the Hubbard model on the geometrically frustrated anisotropic checkerboard lattice at half filling using cellular dynamical mean-field theory. Phase diagrams over a wide area of the parameter space are obtained by varying the interparticle interaction strength, geometric frustration strength, and temperature. Our results show that frustration and thermal fluctuations play a competing role against the interactions and in general favor a metallic phase without antiferromagnetic order. Due to their interplay, the system exhibits competition between antiferromagnetic insulator, antiferromagnetic metal, paramagnetic insulator, and paramagnetic metal phases in the intermediateinteraction regime. In the strong-interaction limit, which reduces to the Heisenberg model, our result is consistent with previous studies.

Bose-Hubbard Model in Checkerboard Superlattices with a Magnetic Field

In this paper we investigate classical and quantum phase transitions of Bose-Hubbard model in checkerboard superlattices with a magnetic field at the mean-field level. By analyzing stability of normal state phase boundaries are obtained analytically for zero and finite temperature in a unified theoretical frame and easily extended to the situation without the magnetic field. All results illustrate that the introduction of the magnetic field enhances the stability of normal state and Mort insulator. In addition we also note that the critical hopping term presents an oscillating behavior inversely following the upper boundary of Hofstadter butterfly.

Effect of visual stimulus locations on pattern-reversal visual evoked potential An epidural electrocorticogram study

To explore the effect of the location of a visual stimulus on neural responses in the primary visual cortex （V1）, a micro-electromechanical system-based microelectrode array with nine channels was implanted on the cerebral dura mater of V1 in adult cats. 2 Hz pattern reversal checkerboard stimul were used to stimulate the four visual quadrants （i.e., upper left, upper right, lower left, and lower right fields）. The results showed that there was a N75 component of the visual evoked potential around 50-80 ms after the onset of a checkerboard stimulus, and the onset of these N75 peaks varied with different stimulus locations. The checkerboard stimuli Jnduced shorter latencJes in the contralateral V1 than in the ipsilateral V1, while the checkerboard stimulus in the upper half visual field induced shorter latencies for N75. These results suggested that the pattern-reversal stimuli induced neural activities in V1 that can be recorded with multichannel microelectrodes, and more detailed temporal and spatial properties can be measured.

NOVEL METHOD SOLVING NUMERICAL INSTABILITIES IN TOPOLOGY OPTIMIZATION

Numerical instabilities are often encountered in FE solution of continuumtopology optimization. The essence of the numerical instabilities is given from the inverse partialdifferential equation (PDE) point of view. On the basis of the strict mathematical theory, a novelmethod, named as window filter and multi-grid method, which solves the numerical instabilities, isproposed. Convergent analyses and a numerical example are presented.

Hofstadter's Butterfly and Phase Transition of Checkerboard Superconducting Network in a Magnetic Field

We study the magnetic effect of the checkerboard superconducting wire network. Based on the de Gennes- Alexader theory, we obtain difference equations for superconducting order parameter in the wire network. Through solving these difference equations, we obtain the eigenvalues, linked to the coherence length, as a function of magnetic field. The diagram of eigenvalues shows a fractal structure, being so-called Hofstadter＇s butterfly. We also calculate and discuss the dependence of the transition temperature of the checkerboard superconducting wire network on the applied magnetic field, which is related to up-edge of the Hofstadter＇s butterfly spectrum.

Wideband radar cross-section reduction using plasma-based checkerboard metasurface

For stealth technology,in order to overcome the limitations of thin-layer plasma for electromagnetic waves attenuation and further broaden the radar cross-section(RCS)reduction(RCSR)band of the metasurface,the plasma-based checkerboard metasurface composed of plasma and checkerboard metasurface is investigated to achieve better RCSR.We designed a checkerboard metasurface which can achieve abnormal reflection to reduce RCS and whose-10d B RCSR bandwidth is from 8.1 to 14.5 GHz,the RCSR principle of it lies in the backscattering cancellation,which depends on the phase difference of artificial magnetic conductor(AMC)units.The designed plasma-based checkerboard metasurface is a thin composite structure,including a checkerboard metasurface,a plasma layer,and an air gap which is between them.Full wave simulations confirm that the plasma-based checkerboard metasurface’s–10 dB RCS reduction bandwidth and RCS reduction amplitude,are both increased under different polarized waves compared with the only single plasma or the only metasurface.We also introduced the reason and mechanism of the interaction between plasma and the checkerboard metasurface to improve the RCSR effect in detail.As plasma-based checkerboard metasurface does not need the plasma to be too thick for plasma stealth,its application in practical scenarios is easier to implement.

Dynamics analysis on transverse cutting mechanism of straw checkerboard paving robot

The transverse cutting mechanism of the checkerboard paving robot, which directly affects the robot＇s operation, is regarded as the most important part in a transverse pavement system This research aims at designing a new system which is appropriate for desert wofidng en- vironments and finishing cutting the rope of straw. In this paper, computer emulating technology is applied, and with three-dimensional modeling by Pro/ENGINEER software, can observe whether or not interference exists. Also, the speed and displacement parameters of the main parts of the cutting system are given by the dynamic emulation by Automatic Dynamic Analysis of Mechanical System （ADAMS）, which theoretically assures the feasibility and appropriateness of the cutting mechanisrn~ Finally, results of the experinaent shows that the cutting mechanism can cut the straw strand as designed.

<i>In Vitro</i>Activity of Colistin and Vancomycin or Azithromycin Combinations on Extensively Drug Resistant <i>Acinetobacter baumannii</i>Clinical Isolates

Background: Extensively drug resistant Acinetobacter baumannii (XDR-AB) presents an increasing challenge to health care in Egypt as they are among the most common bacteria isolated in hospital setting. Treatment of such infections usually involves the use of antimicrobial agents in combination. Various combinations have been proposed, with colistin serving as the backbone in many of them even for colistin resistant isolates. Aim: The study was conducted in order to test the in vitro combined effects of colistin and vancomycin or azithromycin against (XDR-AB) causing infections at Alexandria Main University Hospital in Egypt, in an attempt to detect the possibility of a beneficial combination therapy. Material/Methods: Thirty XDR-AB clinical isolates were included in the study. Antibiotic susceptibility testing was performed using automated Vitek 2 compact system and disc diffusion method. Colistin antibiotic disc diffusion test was compared with broth microdilution method. Organisms were also tested against colistin and vancomycin or azithromycin in combination using checkerboard synergy test and FICI (Fractional Inhibitory Concentration Index) was calculated. Synergy was defined as a FICI of ≤0.5. Results: On comparing the two methods used to detect susceptibility to colistin to broth microdilution for MIC (minimum inhibitory concentration) determination, as a reference method, the Vitek showed 100% categorical agreement (CA), on the other hand, the disc diffusion showed CA of 93% with very major errors. Synergy was detected for all isolates (100%) when combining colistin with vancomycin (FICI mean = 0.08). As for azithromycin, 21 strains had FICI range from 0.7 to 1.001, denoting indifference;the remaining 9 strains showed synergy with FICI range from 0.06 to 0.241. The mean colistin/azithromycin FICI was 0.71 for the 30 isolates. Conclusion: These findings suggest that regimens containing vancomycin may confer therapeutic benefit for infection due to XDR-AB;however, other methods (time-kill assay) should be used to confirm such synergy. Furthermore, the optimal combination treatment for serious XDR-AB infection should be addressed in a prospective clinical trial.

Side information refinement in distributed video coding

Side information （SI） is one of the key issues in distributed video coding （DVC） and affects the compression performance of DVC largely. This paper proposes an SI refinement algorithm, in which the Wyner-Ziv （WZ） frame is split into two parts based on checkerboard pattern, and the two parts are encoded independently but decoded sequentially. In the decoding process, the part 1 is first decoded with the initial SI and partially decoded part （PDP） 1 is used to improve the motion vectors （MVs） and SI of both parts. At the next stage, the part 2 is decoded with the improved SI and PDP 2 is used to further refine MVs of the part 2. Then, SI of both parts are further refined. Simulation results show that the proposed algorithm can improve the peak signal to noise ratio （PSNR） by up to 1.43 dB when compared with traditional DVC codec.

Checkerboard DNA-DNA杂交技术用于G^+致龋菌的分析

Checkerboard DNA-DNA杂交技术(CKB)能利用地高辛(DIG)标记的基因组DNA探针对菌斑样品中的40个菌种同时进行定量分析。此技术最初用于研究龈下菌斑的优势G-菌。本研究的目的是进一步发展此项技术,并把它应用于一个更大范围的潜在致龋菌G+菌和白色念珠菌的分析。

Checkerboard Colourable Twuals

In this article we show that any embedded graph has a checkerboard colourable twual,which is equivalent to having a bipartite twual.We also obtain that any Eulerian embedded graph has a checkerboard colourable partial Petrial,answering questions posed by Ellis-Monaghan and Moffatt[Trans.Amer.Math.Soc.,364,1529–1569(2012)].