First-principles calculations of the YBa2Cu3O7/PrBa2Cu3O7 interface

We discuss results of spin-polarized electronic structure calculations for a 1 × 1 YBa₂Cu₃O₇/PrBa₂Cu₃O₇ supercell, obtained by the full-potential linear augmented plane wave (FLAPW) method as implemented in the WIEN2k package. The calculations are based on the generalized gradient approximation for the exchange correlation functional. The on-site Coulomb interaction of the correlated Cu 3d and Pr 4f electrons is considered by using the LSDA+U approach. The electronic states of the YBa₂Cu₃O₇/PrBa₂Cu₃O₇ interface are compared with the respective states in the PrBa₂Cu₃O₇ and YBa₂Cu₃O₇ bulk compounds, where we focus on the magnetic Pr atoms and the Cu atoms in the CuO₂ planes.     

Plato: A localised orbital based density functional theory code

The Plato package allows both orthogonal and non-orthogonal tight-binding as well as density functional theory (DFT) calculations to be performed within a single framework. The package also provides extensive tools for analysing the results of simulations as well as a number of tools for creating input files. The code is based upon the ideas first discussed in Sankey and Niklewski (1989) [1] with extensions to allow high-quality DFT calculations to be performed. DFT calculations can utilise either the local density approximation or the generalised gradient approximation. Basis sets from minimal basis through to ones containing multiple radial functions per angular momenta and polarisation functions can be used. Illustrations of how the package has been employed are given along with instructions for its utilisation.

Program summary

Program title: PlatoCatalogue identifier: AEFC_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFC_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 219 974No. of bytes in distributed program, including test data, etc.: 1 821 493Distribution format: tar.gzProgramming language: C/MPI and PERLComputer: Apple Macintosh, PC, Unix machinesOperating system: Unix, Linux and Mac OS XHas the code been vectorised or parallelised?: Yes, up to 256 processors testedRAM: Up to 2 Gbytes per processorClassification: 7.3External routines: LAPACK, BLAS and optionally ScaLAPACK, BLACS, PBLAS, FFTWNature of problem: Density functional theory study of electronic structure and total energies of molecules, crystals and surfaces.Solution method: Localised orbital based density functional theory.Restrictions: Tight-binding and density functional theory only, no exact exchange.Unusual features: Both atom centred and uniform meshes available. Can deal with arbitrary angular momenta for orbitals, whilst still retaining Slater–Koster tables for accuracy.Running time: Test cases will run in a few minutes, large calculations may run for several days.     

Molecular dynamics simulations to explore the effect of chemical bonding in the keV bombardment of Si with C60, Ne60 and Ne60 projectiles

Depth profiling experiments using secondary ion spectrometry (SIMS) have shown effects that are characteristic to the pairing of the projectile with a Si target. Previous molecular dynamics simulations demonstrate that this unusual behavior is due to the fact that strong covalent bonds are formed between the C atoms in the projectile and the Si atoms in the target, which result in the implantation of carbon into the solid. The focus of this paper is to understand how the formation of chemical bonds affects the net sputtered yield. The results of molecular dynamics simulations of the keV bombardment of Si with C₆₀, Ne₆₀ and ¹²Ne₆₀ at normal incidence are compared over a range of incident kinetic energies from 5 to 20 keV. The net yields with Ne₆₀ and ¹²Ne₆₀ are significantly greater than with C₆₀ at all incident kinetic energies, with ¹²Ne₆₀ having the largest values. Application of the mesoscale energy deposition footprint (MEDF) model shows that the initial deposition of energy into the substrate is similar with all three projectiles. Snapshots of the initial pathway of the projectile atoms through the substrate show a similar lateral and vertical distribution that is centered in the region of the energy footprint. Therefore, the reason for the reduced yield with C₆₀ is that the C atoms form bonds with the Si atoms, which causes them to remain in the substrate instead of being sputtered.     

MD study on temperature dependence of sputtering yield

Temperature dependence of sputtering yield is studied through molecular dynamics (MD) simulation that is performed for Ag sputtered by 12.6 keV Ar impacting at normal incidence. The target temperature is considered from 300 to 1235 K. It is found that the target temperature has little effect on the monomer yield because it comes from the energetic collision cascade. On the other hand, the sputtered cluster yield increases with the target temperature. It seems that the sputtered cluster is produced due to the thermal spike near the surface and the thermal spike is strongly influenced by the target temperature.     

Monte Carlo study of ion-induced secondary electron emission from SiO2

Here we describe a recently developed direct Monte Carlo program to study kinetic electron emission from SiO₂ target. The program includes excitation of the target electrons (by projectile ions, recoiling target atoms and fast primary electrons), subsequent transport and escape of these electrons from the target surface. The program can be used to calculate the electron yields, distribution of electron excitation points in the target and other physical parameters of the emitted electrons. In order to demonstrate the capabilities of this program, we report a study on the kinetic electron emission from SiO₂ induced by fast (1-10 keV) rare gas ions. The calculated kinetic electron yield for various ion energies and masses is in good agreement with the predictions of most frequently applied theoretical model. In addition, the effects of projectile energy, mass and impact angle on the depth distribution of electron excitation points and average escape depth of the outgoing electrons were investigated. It is important to mention that the existing experimental techniques are not capable to measure these parameters.     

Assessment of approximations for efficient topography simulation of ion beam processes: 10 keV Ar on Si

The main assumption of existing efficient topography simulations is that sputtering is a local process that depends only on the angle of incidence and not on the detailed shape of the surface. If redeposition is considered, sputtered atoms are redeposited and cause no further sputtering when they hit another part of the surface. Furthermore the angular distribution of sputtered atoms follows a cosine law. If ion reflection is considered, ions do not lose energy during backscattering. Using binary collision simulations (IMSIL) and comparing them with results obtained by a topography simulator (IonShaper^®) we show that all these assumptions need refinement for the simulation of nanostructures except the neglect of sputtering by sputtered atoms. In addition we show that a nonlocal model is essential for ion beam induced deposition of narrow structures.     

Optical emission from LiNbO3(:Fe)/porous Si structures

Using pulsed laser deposition, a layer of LiNbO₃(:Fe) film with a thickness of 180 nm was coated onto porous Si (PS) stored in air for 1 year. A photoluminescence (PL) band enhanced about three times was observed at ∼625 nm with a same peak position as that of the stored PS. It is revealed that a new PL excitation band occurs at ∼363 nm, which is nearly equal to the fundamental optical absorption edge position of LiNbO₃. The X-ray diffraction results disclose that the enhancement of the PL intensity is closely related to formation of a textured LiNbO₃ film. Based on spectral analysis, we attribute the enhanced PL to optical transition in the E′ defect centers localized at the surfaces of PS nanocrystals, whereas the photoexcited carriers mainly come from the coated LiNbO₃ film. This kind of LiNbO₃(:Fe)/PS structures is expected to have important applications in modern ferroelectric optoelectronics.     

Linear optical properties of solids within the full-potential linearized augmented planewave method

We present a scheme for the calculation of linear optical properties by the all-electron full-potential linearized augmented planewave (LAPW) method. A summary of the theoretical background for the derivation of the dielectric tensor within the random-phase approximation is provided. The momentum matrix elements are evaluated in detail for the LAPW basis, and the interband as well as the intra-band contributions to the dielectric tensor are given. As an example the formalism is applied to Aluminum. The program is available as a module within the WIEN2k code.     

Small‐Molecule Inhibitors of the Tumor Suppressor Fhit

The tumor suppressor Fhit and its substrate diadenosine triphosphate (Ap₃A) are important factors in cancer development and progression. Fhit has Ap₃A hydrolase activity and cleaves Ap₃A into adenosine monophosphate (AMP) and adenosine diphosphate (ADP); this is believed to terminate Fhit‐mediated signaling. How the catalytic activity of Fhit is regulated and how the Fhit ? Ap₃A complex might exert its growth‐suppressive function remain to be discovered. Small‐molecule inhibitors of the enzymatic activity of Fhit would provide valuable tools for the elucidation of its tumor‐suppressive functions. Here we describe the development of a high‐throughput screen for the identification of such small‐molecule inhibitors of Fhit. Two clusters of inhibitors that decreased the activity of Fhit by at least 90 % were identified. Several derivatives were synthesized and exhibited in vitro IC₅₀ values in the nanomolar range.     

机械振动信号内在模式的复杂性评估

针对机械振动信号非平稳特性,利用经验模式分解法将其分解为若干个内在的振荡模式（即基本模式分量）,从而使得不同的基本模式包含有不同的设备状态信息。借助近似熵的概念,可定理描述原始信号和各振荡模式的复杂性,实现对机械振动信号内在模式复杂性的定理评估。该方法不仅有助于揭示和认识转子系统的复杂动力学行为,还能有效地监测系统状态的早期变化,及时捕捉机组潜在的隐患,预防故障的升级恶化。工程应用实例表明,该方法可有效提取机组的故障信息,从而为机械设备状态监测和故障诊断提供一种行之有效的新方法。