Analysis of non-photonic electrons in Cu + Cu collisions at $\sqrt{s_{NN}}=200$ GeV

Heavy-flavor semileptonic decays are expected to dominate the spectrum of non-photonic electrons produced from collisions at the energies of the Relativistic Heavy Ion Collider. The non-photonic electron yield is suppressed by approximately a factor of 5 in central Au + Au events at  GeV relative to p+p events with the same collision energy. Most theoretical models predict less non-photonic-electron suppression than is observed experimentally. We present a preliminary measurement of the yield of non-photonic electrons in Cu + Cu events at  GeV, as well as the nuclear modification factor.     

Generation of a Sub-10fs Laser Pulse by a Ring Oscillator with a High Repetition Rate

A compact femtosecond Ti：sapphire ring oscillator composed of chirped mirrors is designed. By accurately optimizing the intra-cavity dispersion and the mode locking range of the ring configuration, we generate laser pulses as short as 7.7fs with a repetition rate as high as 745 MHz. The spectrum spans from 660nm to 94Ohm and the average output power is 480mW under the cw pump laser of 7.5 W.     

Generation of 170-fs Laser Pulses at 1053nm by a Passively Mode-Locked Yb:YAG Laser

A novel method is developed to obtain 1.05μm laser operation with a Yb：YAG laser. By using a Yb：YAG crystal with proper length and doping concentration, a femtosecond Yb： YAG laser is realized at the central wavelength of 1053nm. The measured pulse duration and spectral bandwidth （FWHM） are 170fs and 7nm; the repetition rate is 80 MHz. Under a power pump of 2 W, an average mode-locking power of 180mW is achieved.     

Investigations of the optical and EPR spectra for (NiX6) (X=Cl, Br, I) clusters

In this paper, the formulae of optical spectral levels and electron paramagnetic resonance (EPR) spectra in trigonal symmetry of 3d⁸ ions are established on the basis of strong field mechanism and a two spin-coupling (SO) parameters model. Unlike the classical crystal-field approach which has only taken the SO coupling of the central metal ions into account, the contribution of the SO coupling of the ligand ions to the optical and EPR spectra has been included in these formulae. When the optical and EPR spectra of the strong covalent crystals are calculated, the reasonable results can be obtained if the two SO parameters model has been put into action. As an application, the optical and EPR spectra of the (NiX₆)⁴⁻ clusters in CsMgX₃:Ni²⁺ (X=Cl, Br, I) crystals have been studied by the complete diagonalization (of energy matrix) method (CDM). The calculated results agree well with experimental findings. From the investigations, a more valid method to calculate the optical and EPR spectra for 3d⁸ ions clusters is provided.     

Purification of human immunoglobulin G via Fc-specific small peptide ligand affinity chromatography

Chromatographic resins of a family of linear Fc-binding hexamer peptides (HWRGWV, HYFKFD, and HFRRHL) exhibited the ability to selectively adsorb and isolate human IgG (hIgG) from complete mammalian cell culture medium (cMEM). Among them, the HWRGWV resin with a peptide density of 0.08 mequiv./g of resin was able to purify hIgG from cMEM with both purity and yield as high as 95%, comparable to Protein A and A2P agarose gels. The influences of N-terminal acetylation of the HWRGWV resin, ligand density on the resin, initial hIgG concentration, and temperature on IgG isolation were also investigated. The results indicate that these small peptide ligands, especially HWRGWV, offer a potential alternative to the use of Protein A or Protein G for large scale affinity chromatography.     

Crystal field and microscopic spin Hamiltonians approach including spin-spin and spin-other-orbit interactions for d and d ions at low symmetry C3 symmetry sites: V in Al2O3

A new module has been developed within the CFA/MSH computer package, which is applicable for d² and d⁸ ions at sites of trigonal symmetry type I (C_3v,D₃,D_3d) and type II (C₃,C_3i), including the ‘imaginary’ CF term. For the first time the spin-spin (SS) and spin-other-orbit (SOO) interactions have also been included in the Hamiltonian. This module enables to study the contributions to the energy levels and the spin Hamiltonian parameters, i.e. zero-field splitting D and g-factors: g_∥ and g_⊥. The contributions arising from the spin-orbit (SO), SS, and SOO interaction as well as those due to the low symmetry CF effects induced by the distortion angle ?, which describes the difference between C₃ and C_3v symmetry, can be studied. As an application of the new module, calculations have been carried out for V³⁺(3d²) ions in α-Al₂O₃ crystal, taking into account for the first time the SS and SOO interactions, and the low symmetry CF effects. The results show that (i) the contributions from the SS and SOO interactions to the energy levels are larger for free V³⁺ ions than those for V³⁺ ions in α-Al₂O₃ crystal, (ii) both the contributions to the SH parameters and the energy levels arising from the SOO interaction are larger than those arising from the SS interaction, (iii) the contributions due to the low symmetry CF effects induced by the distortion angle ? are in general significant, (iv) D and g_⊥ are sensitive to the distortion angle ?, whereas g_∥ is insensitive to ?, and (v) the influence of the lattice distortions on the spectroscopic properties of V³⁺ ion in α-Al₂O₃ is pronounced. It appears important for similar ion-crystal cases to consider the lattice distortions in detailed calculations, which take into account the relevant contributions from the SO, SS and SOO interactions. A good agreement between the theoretical and experimental results has been obtained.     

Single crystal EPR spectrum of Cr3+ in lanthanum lutecium gallium garnet

The Cr³⁺ EPR spectra of YAG type crystals normally consist of four peaks whose positions are dependent on the axial zero-field splitting D with axis along a 111 direction and angle between that direction and the applied field H ₀. In LLGG only three principal peaks are observed with zero-field axis nearly along x, y or z. This anomaly is attributed to the relatively small size of Cr³⁺ compared to Lu³⁺ which it displaces in an octahedral site. D varies slightly for the different zero-field axes: 0.480 cm^–1 along x, 0.429 cm^–1 along y and 0.470 cm^–1 along z. The spectroscopic splitting factor g=1.978±0.001 is essentially isotropic and independent of axes within the experimental error.     

Single fluorescence centers on the tips of crystal needles: First observation and prospects for application in scanning one-atom fluorescence microscopy

A scanning optical fluorescence microscope is suggested, whose active element (needle) is made of a crystal containing impurity ions or color centers subject to excitation by laser radiation. The excitation energy from a single impurity center at the very tip of the needle is transferred by the resonance dipole-dipole exchange mechanism to fluorescence centers on the surface of the sample under study. It is demonstrated that this approach can help attain a nanometer-high spatial resolution at a high sensitivity substantially exceeding in some cases the sensitivity of the standard near-field fluorescence microscopy technique. Various crystals and impurity centers, potentially most suitable for the implementation of the method under consideration, are briefly analyzed. Information is presented on the manufacture of sharp-pointed needles from LiF crystals containing F₂-centers and the first observation of single F₂-centers on their tips by the laser-photoelectron projection microscopy technique, which allows one to speak of the practical creation of the first active elements for the microscope suggested.Dedicated to Prof. F. P. Schäfer on the occasion of his 65th birthday.