Observation of magnetic breakdown in double quantum wells

We report on our studies of magnetic breakdown (MB) in coupled GaAs/Al_0.3Ga_0.7As double quantum wells (DQWs) subject to crossed magnetic fields. MB is a failure of semiclassical theory that occurs when a magnetic field causes electrons to tunnel across a gap ink-space from one Fermi surface (FS) branch to another. We study MB in a two-branch FS created by subjecting a DQW to an in-plane magnetic field (B_∥). The principal effect ofB_∥is a distortion in the dispersion curve of the system, yielding a FS consisting of two components, a lens-shaped inner orbit and an hour-glass-shaped outer orbit. The perpendicular field (B_⊥) causes Landau level formation and Shubnikov–de Haas (SdH) oscillations for each branch of the FS. At higher perpendicular fields MB occurs and electrons tunnel throughk-space from one FS orbit to the other. MB is observed by noting which peaks are present in the Fourier power spectrum of the magnetoresistance versus 1/B_⊥at constantB_∥. We observe MB in two DQW samples over a range ofB_∥.     

Visible light activated photo-catalytic effect and local structure of iron silicate glass prepared by sol-gel method

A relationship between methylene blue (MB) decomposition ability under visible light and local structure of xFe₂O₃·(100-x)SiO₂ glass abbreviated as xFS prepared by sol-gel method was investigated by ⁵⁷Fe-Mössbauer spectroscopy, X-ray diffractometry (XRD) and ultraviolet-visible light absorption spectroscopy (UV-Vis). Mössbauer spectra of xFS glass with x of 10, 30 and 50 annealed at 1000 °C for 3 h were mainly composed of a paramagnetic doublet due to fayalite (Fe₂SiO₄), and magnetic sextets due to magnetite (Fe₃O₄) or hematite (α-Fe₂O₃). The absorption area (A) of α-Fe₂O₃ gradually increased from 0.0 to 10.3 and 100 % with the increasing Fe₂O₃ content (x) of annealed xFS glass. A leaching test performed by 20 mL of MB aqueous solution and 40 mg of annealed 50FS glass showed that MB concentration decreased from 16.2 to 4.7 μmol L^?1 after 2 h with the first order rate constant of 1.8 × 10^?4 s^?1. These results prove that annealed iron silicate glass containing α-Fe₂O₃ can decompose MB effectively under visible light irradiation.     

Thermal characterisation of dye-intercalated K-10 montmorillonite ceramics using photoacoustic technique

Thermal diffusivity (TD) measurements were performed on some industrially important dyes – auramine O (AO), malachite green and methylene blue (MB) – adsorbed K-10 montmorillonites using photoacoustic method. The TD value for the dye-adsorbed clay mineral was observed to change with a variation in dye concentration. The contribution of the dye towards TD was also determined. The repeatedly adsorbed samples with MB and AO exhibited a lower TD than the single-adsorbed samples. TD values of sintered MB samples were also obtained experimentally. These sintered samples exhibit a higher TD, although they show a trend similar to that of non-sintered pellets. A variation in dye concentration and sintering temperature can be used for tuning the TD value of the clay mineral to the desired level.     

Simple dose rate measurements for a very high synchrotron X‐ray flux

Dose measurements based on methylene blue (MB) bleaching, widely used for ultraviolet light, can also be applied to X‐rays including very high flux levels. This method has been tested by using both MB bleaching and Fricke dosimetry for a conventional monochromatic X‐ray source and then for `white‐beam' synchrotron radiation. The results show that MB bleaching dosimetry can easily measure X‐ray doses up to at least 10⁵ Gy s^?1, as long as the MB concentration is sufficiently high. This condition can be verified from the deviations from linearity of the bleaching versus exposure time.     

拓扑绝缘基铁磁/铁磁超导隧道结的磁效应和塞曼效应(英文)

运用拓展的BTK理论研究了拓扑绝缘层上铁磁/铁磁超导隧道结的磁效应和塞曼效应,同时考虑了铁磁体和铁磁超导体之间的费米能级错配效应.研究发现:在该系统中塞曼效应和邻近效应可以共存;铁磁体和铁磁超导体之间的费米能级错配效应能够增强系统中发生在eV=Δ处的Andreev谐振散射过程和邻近效应.     

On the possibility of dark energy from corrections to the Wheeler–DeWitt equation

We present a method for approximating the effective consequence of generic quantum gravity corrections to the Wheeler–DeWitt equation. We show that in many cases these corrections can produce departures from classical physics at large scales and that this behaviour can be interpreted as additional matter components. This opens up the possibility that dark energy (and possible dark matter) could be large scale manifestations of quantum gravity corrections to classical general relativity. As a specific example we examine the first order corrections to the Wheeler–DeWitt equation arising from loop quantum cosmology in the absence of lattice refinement and show how the ultimate breakdown in large scale physics occurs.     

Quantum Boltzmann equation solved by Monte Carlo method for nano-scale semiconductor devices simulation

A two-dimensional (2D) full band self-consistent ensemble Monte Carlo (MC) method for solving the quantum Boltzmann equation, including collision broadening and quantum potential corrections, is developed to extend the MC method to the study of nano-scale semiconductor devices with obvious quantum mechanical (QM) effects. The quantum effects both in real space and momentum space in nano-scale semiconductor devices can be simulated. The effective mobility in the inversion layer of n and p channel MOSFET is simulated and compared with experimental data to verify this method. With this method 50nm ultra thin body silicon on insulator MOSFET are simulated. Results indicate that this method can be used to simulate the 2D QM effects in semiconductor devices including tunnelling effect.     

美兰光化学法对红细胞损伤的NMR研究

运用³¹P NMR研究红细胞中高能磷酸化合物的代谢变化,探讨美兰光化学法对红细胞的损伤. 采用MSL-300 MHz型超导核磁共振仪分别测量健康成人红细胞对照组、经美兰（亚甲基蓝）光化学处理组及预先加入L-组氨酸组的高能磷酸化合物,通过分析比较红细胞中2,3-二磷酸甘油酸（2,3-DPG）、三磷酸腺苷（ATP）及磷酸化糖（SP）相对含量,了解美兰光化学法对红细胞代谢的影响. 经亚美兰光化学法处理的红细胞,葡萄糖进入戊糖磷酸途径的分量增加,使红细胞中2,3-DPG和ATP含量显著减少,而SP含量大幅上升,在某种程度上影响红细胞的理化性质和功能指标;L-组氨酸对此有一定的保护作用.     

Magnitude of O(α2) corrections and search for new effects in the electroweak interactions

A quick method of calculating certain combinations of the O(α²) corrections in the electroweak theory is presented. The results agree with earlier explicit calculations of the O(α²) corrections to the vector boson masses and in other cases provide an estimate of the lower limits for such corrections. Some non-standard effects like heavy fermion or supersymmetric contributions are also discussed. Detailed calculations show that even in the case of the strong supersymmetric contribution, the new one-loop corrections are comparable to the two-loop ones in the standard model.     

高剥离类钠离子3s2S—3d2电四极矩E2光谱跃迁的理论计算

 利用全相对论性多组态Dirac-Fock平均能级方法系统地计算了高剥离类钠离子3s²S—3d²D(Z=14～103）电四极矩E2光谱跃迁的能级间隔，跃迁几率和振子强度，计算中考虑了核的有限体积效应，Breit修正和QED修正，所得结果和最近的实验数据及理论计算值进行了比较，计算结果表明：高原子序数的高荷电离子的电四极矩E2光谱跃迁的跃迁几率和中性原子的电偶极E1的相当，在ICF和MCF高温高密度激光等离子体中，电四极矩E2光谱跃迁过程不容被忽视。     

Pion pair production with higher order radiative corrections in low energy $e^+e^-$ collisions

The complete QED initial state (IS), final state (FS) and initial–final state (IFS) interference corrections to the process are presented. Analytic formulae are given for the virtual and for the real photon corrections. The total cross section (), the pion angular distribution () and the invariant mass distribution () are investigated in the regime of experimentally realistic kinematical cuts. It is shown that in addition to the full corrections also the and leading-log photonic corrections as well as the contributions from IS -pair production have to be taken into account if at least per cent accuracy is required. For the data analysis we focus on an inclusive treatment of all photons. The theoretical error concerning our treatment of radiative corrections is then estimated to be 2 per mill for both the measurement of the total cross section and the invariant mass distribution. In addition we discuss the model uncertainty due to the pion substructure. Altogether the precision of the theoretical prediction matches the requirements of low energy experiments like the ones going on at DANE or VEPP-2M. Received: 6 September 2001 / Revised version: 24 January 2002 / Published online: 5 April 2002     

Corrections to the density-functional theory electronic spectrum: copper phthalocyanine

A method for improving the electronic spectrum of standard Density-Functional Theory (DFT) calculations (i.e., LDA or GGA approximations) is presented, and its application is discussed for the case of the copper phthalocyanine (CuPc) molecule. The method is based on a treatment of exchange and correlation in a many-body Hamiltonian, and it leads to easy-to-evaluate corrections to the DFT eigenvalues. Self-interaction is largely corrected, so that the modified energy levels do not suffer from spurious crossings, as often encountered for CuPc in DFT, and they remedy the standard underestimation of the gap. As a specific example we study the sequence and position of the CuPc molecular orbitals, which are wrongly calculated by standard DFT, and show that they are correctly reproduced after our corrections are included. The suggested method is fast and simple and, while not as accurate as hybrid or semiempirical functionals for molecular levels, it can be easily applied to any local-orbital DFT approach, improving on several important limitations of standard DFT methods.     

Fundamental Solutions of the Axial Symmetric Goursat Problem

Abstract

Fundamental solutions (FS) with a given boundary condition on the characteristics of relativistic problems with axial symmetry are considered. This is so-called the Goursat problem (GP) or zero plane formalism in Dirac’s terminology, or modification of the proper time method in the Fock-Nambu-Schwinger formalism (FNS).

Closed FS for the Volkov problem from the point of view of GP can be found. This means that integration over proper time in a FNS integral transformation can be performed. Using the special chosen dynamic symmetry of the initial state, FS for a particle in constant magnetic or constant electric field may also be calculated.     

Complete Fermi surface in BaFe2As2 observed via Shubnikov-de Haas oscillation measurements on detwinned single crystals

We show that the Fermi surface (FS) in the antiferromagnetic phase of BaFe(2)As(2) is composed of one hole and two electron pockets, all of which are three dimensional and closed, in sharp contrast to the FS observed by angle-resolved photoemission spectroscopy. Considerations on the carrier compensation and Sommerfeld coefficient rule out existence of unobserved FS pockets of significant sizes. A standard band structure calculation reasonably accounts for the observed FS, despite the overestimated ordered moment. The mass enhancement, the ratio of the effective mass to the band mass, is 2-3.     

Array illumination with minimal non-uniformity based on generalized phase contrast

The generalized phase contrast method (GPC) has been previously shown to be an efficient technique for generating array illumination and is thus highly suitable for such applications as dynamic multiple beam trapping and optical micromanipulation. However, projected arrays usually exhibit intensity roll-offs that may be undesirable for some applications. We show that the uniformity of GPC-generated array illuminations can be improved using intuitive corrections to the input spatial phase modulation, by increasing or decreasing it to respectively raise or lower the intensity of the corresponding output spots to improve uniformity. This is combined with matching corrections to the phase shift introduced by the phase contrast filter. Results from numerical experiments show that the array illumination uniformity error improves from over 40% to less than 1% while maintaining the efficiency prior to implementing corrections.     

Corrections to the classical continuity boundary conditions at the interface of a composite medium

Using the multiple-scales homogenization method, we derive generalized sheet transition conditions (GSTCs) for electromagnetic fields at the interface between two media, one of which is free-space and the other a certain type of composite material. The parameters in these new boundary conditions are interpreted as effective electric and magnetic surface susceptibilities, which themselves are related to the geometry of the scatterers that constitute the composite. We show that the effective tangential E and H fields are not continuous across the interface except in the limit when the lattice constant (the spacing between the scatterers—atoms, molecules or inclusions in the case of a composite material) of the composite medium is very small compared to a wavelength. We derive first-order corrections to the classical continuity conditions. For naturally occurring materials whose lattice constants are on an atomic scale, these effects are shown to be negligible for waves at optical frequencies or lower. However, once the lattice constant becomes a significant fraction of a wavelength (which is the case for many artificial dielectrics and metamaterials), the corrections can be important. In previous work we have alluded to the fact that such a GSTC is needed to correctly account for the surface effects when extracting the effective material properties of a metamaterial. The results of this current paper justify the assumptions made in that previous work. In general, these GSTCs will result in corrections to the classical Fresnel reflection and transmission coefficients (which are themselves merely zeroth-order approximations to the actual reflection and transmission coefficients), and in a separate publication we will use these GSTCs to address this issue.     

Correcting for incomplete saturation and off-resonance effects in multiple-site saturation-transfer kinetic measurements

The effects of incomplete saturation and off-resonance irradiation on nuclear magnetic resonance saturation-transfer measurements of three-site chemical-exchange rates are discussed. A new method that uses double-saturation measurements is compared with two published methods, one that uses single-saturation measurements and one that uses a single-saturation measurement and a double-saturation measurement. Several formulas are compared for measuring the exchange rate constant k(DE) for exchange from a detected spin D to an exchanging spin E in the presence of exchange from spin D to a competing spin C. For each method, formulas are derived with corrections for incomplete saturation or off-resonance effects, with both corrections, and with neither correction. Exact formulas are available for three exchanging sites with incomplete saturation if there are no off-resonance effects. Off-resonance corrections are imperfect even with complete saturation.     

Cluster calculations for tetrahedrally bonded amorphous semiconductors

It is shown that no computer manageable sample cluster is large enough to eliminate size effects in the calculations of the density of states (DOS) for tetrahedrally bonded amorphous semiconductors. A method which correctly reduces such effects is described. Special attention is given to the anisotropy of the bulk structure, and to the surface bonds. The size sensitive energy regions are identified and further corrections are made. With this method, we can confidently compare the details of the DOS for different existing model structures.     

Multilevel region of interest guided bit allocation for multiview video coding

Multiview video coding (MVC) is an efficient compression scheme, by which the large amount of multiview video data can be effectively processed. However, it ignores the characteristics of the human visual system. In this paper, we propose a multilevel region of interest (ROI) based bit allocation strategy for MVC, which can take advantage of the visual redundancy to improve encoding efficiency. First, the macro block (MB) saliency is derived from depth information of the video sequence, and the multilevel ROI segmentation is conducted based on the MB saliency distribution. Then, the multiview video bit allocation strategy based on multilevel ROI is proposed. We have evaluated system performance with several multiview video sequences in JMVC 8.5 reference software. Experimental results show that the quality of ROIs has a considerable improvement when the bit rate consumed is kept consistent with JMVC. Meanwhile, the proposed MVC method can save bit rate while maintaining the overall image quality.     

Threshold effects on renormalization group running of neutrino parameters in the low-scale seesaw model

We show that, in the low-scale type-I seesaw model, renormalization group running of neutrino parameters may lead to significant modifications of the leptonic mixing angles in view of so-called seesaw threshold effects. Especially, we derive analytical formulas for radiative corrections to neutrino parameters in crossing the different seesaw thresholds, and show that there may exist enhancement factors efficiently boosting the renormalization group running of the leptonic mixing angles. We find that, as a result of the seesaw threshold corrections to the leptonic mixing angles, various flavor symmetric mixing patterns (e.g., bi-maximal and tri-bimaximal mixing patterns) can be easily accommodated at relatively low energy scales, which is well within the reach of running and forthcoming experiments (e.g., the LHC).