Interaction between localized moments in dilute alloys: Correlation effects

The effect of including dynamical correlations between electrons of opposite spins in determining the ground state energy of a pair of magnetically interacting impurity atoms in an otherwise normal metal is discussed. It is found that in the ground state of such a system the spins of the magnetic impurity atoms are aligned antiparallel. In other words, the interaction between the localized states is of antiferromagnetic exchange type. This result differs sharply from that predicted by the Hartree-Fock (H-F) theory, in which the ground state of the system can be either ferro- or antiferromagnetic, depending on the energies of the spin up and spin down electrons relative to the Fermi energy. The calculations are performed using many-body Green's function techniques in thet-matrix approximation.     

Optical properties of nanocrystalline silver halides

A review of quantum confinement effects in nanocrystals of silver bromide (AgBr) and silver iodide (AgI) is presented. AgBr is an indirect gap semiconductor while AgI has a direct band-to-band lowest energy transition. An examination of the low-temperature optical properties of quantum confined AgBr grown using a variety of synthetic techniques will be made. The dynamics of some of the involved excitonic processes will be measured and discussed in reference to a possible breakdown in the momentum selection rules as the nanocrystals are made smaller. Other explanations for this behavior such as impurity exclusion and surface effects will also be considered, as will the dynamics associated with the trapping of excitons at intrinsic iodide impurities in AgBr. Absorption measurements on AgI nanocrystals will be discussed and compared with the exciton photophysics in AgBr. Both AgBr and AgI display an increasing blue shift of their luminescence, arising from the recombination of excitons, as the crystallite size decreases. The luminescence intensity arising from this process increases with decreasing size in AgBr but it disappears in small crystals of AgI. This leads to the conclusion that in the latter material nonradiative decay channels are opening up as the size decreases.     

HT-6M托卡马克等离子体紫外-可见谱

利用光学多道分析仪(OMA)拍摄了HT-6M托卡马克等离子体近紫外可见谱.系统分析了杂质行为,给出了主要杂质碳和氧的朝内的通量,在简化模型下计算了碳氧的化学溅射率,并由此得出碳氧杂质产生机制和可能的循环途径.结果表明,氧杂质在循环途径中起关键性的作用,控制氧杂质尤其重要.     

Ion implantation

Some developments in applications of Mössbauer spectroscopy to investigate ion-implanted radioactive source isotopes in solids are presented. Emphasis is layed on impurity and defect studies in metals and semiconductors. The particular role of Mössbauer spectroscopy in comparison to and in combination with other analytical techniques is illustrated. Recently developed on-line implantation techniques are described, their merits and prospects are discussed.     

用钛吸气方法改善HL-1装置的等离子体性能

用钛吸气方法减少了HL-1托卡马克等离子体中的杂质和气体再循环率,使Z_(eff)降低到1.6;在程序控制送气技术的配合下,有效地控制了密度变化,获得线平均密度元_max=4.9×10~(19)m~(-3)的较高密度的稳定放电;成功地扩展了运行参数空间。     

Two-equivalent and one-equivalent surface states

Two concepts are discussed for the control of semiconductor surface properties by chemical surface state additives. The first is that additives can be used which lead to both filled and empty states, and both are required to control the surface Fermi level. Chemically this is equivalent to adding the impurity in two different oxidation states (valences). It is shown that if one uses this approach, accurate control of the surface Fermi level should be possible for stable systems. The second concept is that it is important to distinguish between two-equivalent and one-equivalent species for use as surface states. The former are chemicals in which a relatively unstable oxidation state exists between the stable oxidation states of interest. The latter (one-equivalent) are chemicals with adjacent stable oxidation states, i.e. stable forms separated by only one electronic charge. Analysis shows that two-equivalent impurities often will behave like minority carrier trapping centers.     

Enhancement of next-nearest-neighbouring entanglement in quantum Ising spin chain

Using the method of the Jordan--Wigner transformation for solving different spin--spin correlation functions, we have investigated the generation of next-nearest-neighbouring entanglement in a one-dimensional quantum Ising spin chain with the Gaussian distribution impurities of exchange couplings and external magnetic fields taken into account. The maximal value of entanglement between the next-nearest-neighbouring qubits in the transverse Ising model was analysed in detail by varying the effectively controlled parameters such as interchange coupling, magnetic field and the system impurity. For such systems, where both exchange couplings and external magnetic field disorder appear, we show that it is possible to achieve next-nearest-neighbouring entanglement better than the previously discussed pure Ising spin chain case. We also show that the Gaussian distribution impurity can induce next-nearest-neighbouring entanglement, which can be used as a means to characterize quantum phase transition.     

含杂质的三臂环中的持续电流

采用量子波导理论,研究了含杂质的介观三臂环中的持续电流。结果表明:输运电流存在时,不含磁场的三臂环中也可有持续电流产生, 这是纯的量子现象。即使含杂质的三臂环和含杂质的单环上、下臂比例相同,两环中的电流也明显不同。更重要的是发现在某些能量范围内,杂质不总是制约持续电流的增大。     

Applications of near infrared spectroscopy in cotton impurity and fiber quality detection: A review

Near infrared spectroscopy (NIRS) is an emerging, non-invasive, multi-index, simple preparation of sample process analytical technique suitable for cotton quality assessment. Cotton impurities not only affect the quality of seed cotton and lint cotton but also the quality of textiles. These impurities can occur during harvest and in the stage of postharvest handing, especially during pack house operations. In such a global and competitive marketplace, it is necessary to explore rapid, accurate, and precise cotton quality measurement techniques which require less expensive instrumentation, exhibit increased flexibility versatility, and perform both laboratory measurements and non-laboratory (at-line or field) measurements. Some reports have been published on the use of NIRS technology for inspecting cotton impurity contents, micronaire, and cotton fiber quality. This article condenses a representative selection of recent research in order to observe the significant progresses in how NIRS technology is applied to inspection of cotton impurity and cotton fiber. Additionally, the drawbacks and obstacles of NIRS for quality measurement in cotton are summarized and the trends are discussed.     

Investigations of Impurity Atom Deposition in the Limiter Shadow of the T-10 Tokamak by Means of Auger Electron Spectroscopy

The impurity flux in the limiter shadow region of the T-10 tokamak has been studied by exposing a solid probe to the plasma and subsequent investigation of deposits by surface analysis techniques. The main constitutents of the inner construction materials of T-10 could be detected by AES and SIMS. The deposited amount of impurities has been shown to rise with a decrease of the distance between probe and plasma. Long term observations of the metal impurity composition in the limiter shadow region by means of the deposition probe have shown a gradual decrease of the relative Ni concentration, which is explained as a successive deposition of stainless steel limiter material on the Inconel liner. The observed spatial asymmetry of the impurity flux and the deposition profiles for different elements on the probe are discussed.     

含顺磁杂质超导体中的束缚态

本文利用广义正则变换和自洽场方法,讨论了单个杂质对超导体的影响。证明在磁性杂质附近,可能形成一个束缚态的元激发,其能量位于能隙之中。求出了能级和波函数的解析表达式,并计算了束缚能级所引起的附加电磁吸收。讨论了与此有关的隧道和高频吸收实验。此外,还讨论了非磁性杂质对连续谱元激发的影响及杂质附近能隙的变化。     

A theoretical study of alkaline-earth cations in crystalline sodium chloride,potassium chloride and potassium bromide

Theoretical methods, based on Mott-Littleton techniques are used to investigate the defect structures of alkali-halide crystals doped with divalent ions. The systems studied are those having Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ as impurity ions in NaCl, KCl and KBr crystals. Our calculations find comparable stability of the (110) nearest-neighbour and (200) next-nearest-neighbour complexes whereas the (211) complex is found to be less stable. Significant trends in the variation of binding energy with dopant ion radius are predicted. We also consider the activation energies for the w₁, w₂, w₃ and w₄ type jumps which occur in the vicinity of the impurity ion. The results are, where possible, compared with experimentally determined defect energies and their implications in diffusion processes of M²⁺ impurities in the alkali halides are discussed.     

平行速度剪切驱动湍流引起的粒子输运

通过离子温度梯度及平行速度剪切的准线性湍流理论，得到了由杂质离子及抵频E×B湍流所驱动的径向离子流及相应的输运系数．理论分析表明，主要离子和杂质离子的径向离子流具有相反的方向，并随着平衡流速剪切以及杂质离子的密度梯度的变化而改变．增强平行速度剪切对主要离子的约束可产生有利影响 关键词：     

Quantum phase transitions in the bosonic single-impurity Anderson model

We consider a quantum impurity model in which a bosonic impurity level is coupled to a non-interacting bosonic bath, with the bosons at the impurity site subject to a local Coulomb repulsion U. Numerical renormalization group calculations for this bosonic single-impurity Anderson model reveal a zero-temperature phase diagram where Mott phases with reduced charge fluctuations are separated from a Bose-Einstein condensed phase by lines of quantum critical points. We discuss possible realizations of this model, such as atomic quantum dots in optical lattices. Furthermore, the bosonic single-impurity Anderson model appears as an effective impurity model in a dynamical mean-field theory of the Bose-Hubbard model.     

Nitrogen in diamond studied by magnetic resonance

Nitrogen is the most common substitutional impurity in diamond. Much of the information about the many different defects in diamond containing nitrogen atoms has been found by magnetic resonance. This information is reviewed, and the possibility is discussed of finding information about more such centres, mechanisms of their formation and alteration by external influences. The unambiguously identified centres involve either: (a) only substitutional nitrogen atoms, up to three in number, (b) a combination, of substitutional nitrogen atoms and vacancies, (c) substitutional nitrogen and other foreign atoms. Speculations are made about the atomic models of less well characterized centres, as well as about some simple possible centres which have not yet been identified.     

Electroluminescence of CaSO4: Sm phosphors

CaSO₄ phosphors activated with Sm³⁺ impurity in varying concentrations have been prepared and their electroluminescence systematically studied. The voltage and frequency dependence of brightness is discussed and conclusions are drawn regarding the possible mechanism involved in the process.     

ESR spectroscopy as a tool for identifying joining fragments of antique marbles: the example of a pulpit by Donatello and Michelozzo

ESR spectroscopy is one of the physicochemical techniques used to characterize archaeological white marbles and obtain information about their quarries of provenance. This is done by measuring selected spectral features of the Mn(2+) impurity ubiquitously present in marbles and developing a statistical classification rule from the variable vectors measured for a significant number of samples of known provenance (the quarry database). Now we show that the overall variability exhibited by the same spectroscopic features decreases rapidly with the linear dimensions of the sampled block and can be used to distinguish fragments belonging to the same piece of stone from those simply originating from the same quarry. Application of the method to the seven marble panels of the Donatello pulpit in Prato (Tuscany) shows that they have all been cut from the same single block and their different degradation must be ascribed to differential weathering and to the different conservation treatments undergone in the past. The limits and possible drawbacks of the method are also discussed.     

The Effect of Impurities in a Three-Qubit Ising Spin Model

The dynamics of genuine three-qubit entanglement in Ising spin model is investigated under the effect of impurities with different sites. The analytic expression for the three-tangle measurement is obtained. Results show that the impurity parameters exert great effect on the entanglement value. When the impurity on the boundary sit of the spin chain, the positive contribution of the impurity coefficient on the exchange interaction is greater, the stay time in the greater entanglement is longer. When the impurity sitting in the spin chain, the entanglement variation is periodic with the evolution time only at some given impurity coefficient. The realization of efficient control of the entanglement by appropriate combinations of the tunable parameters should be possible.     

First principle calculations of thermodynamic properties of pure graphene sheet and graphene sheets with Si,Ge,Fe,and Co impurities

The thermal properties of pure graphene and graphene–impurity(impurity = Fe,Co,Si,and Ge) sheets have been investigated at various pressures(0–7 GPa) and temperatures(0–900 K).Some basic thermodynamic quantities such as bulk modulus,coefficient of volume thermal expansion,heat capacities at constant pressure and constant volume of these sheets as a function of temperature and pressure are discussed.Furthermore,the effect of the impurity density and tensile strain on the thermodynamic properties of these sheets are investigated.All of these calculations are performed based on the density functional theory and full quasi harmonic approximation.     

Photon antibunching in resonance fluorescence from impurity atoms in solids

The experimental conditions under which the intensity correlation function of resonance fluorescence of a single atom in a gas may be observed are briefly discussed. In general they can complicate the direct observation of photon antibunching. A direct observation should be possible in the case of a single impurity atom in a solid state matrix. The corresponding intensity correlation function is given.