Double ionization of helium in collision with 20-500-keV/amu Cq+ and Oq+ (q=1-3) ions

Target ionization and projectile charge changing were investigated for 20-500 keV/u Cq+, Oq++He (q=1-3) collisions. Double- to single-ionization ratios R-21 of helium associated with no projectile charge change (direct ionization), single-electron capture, and single-electron loss were measured. The cross-section ratio R-21 depends strongly on the collision velocity v, the projectile charge state q, and the outgoing reaction channel. Meanwhile, a model extended from our previous work [J. X. Shao, X. M. Chen, and B. W. Ding, Phys. Rev. A 75, 012701 (2007)] is presented to interpret the above-mentioned dependences. Good agreement is found between the model and the experimental data.

Slow isocharged sequence ions with helium collisions: Projectile core dependence

The collisions of the isocharged sequence ions of q=6 (C6+, N6+, O6+, F6+, Ne6+, Ar6+, and Ca6+), q=7 (F7+, Ne7+, S7+, Ar7+, and Ca7+), q=8 (F8+, Ne8+, Ar8+, and Ca8+), q=9 (F9+, Ne9+, Si9+, S9+, Ar9+, and Ca9+) and q=11 (Si11+, Ar11+, and Ca11+) with helium at the same velocities were investigated. The cross-section ratios of the double-electron transfer (DET) to the single-electron capture (SEC) sigma(DET)/sigma(SEC) and the true double-electron capture (TDC) to the double-electron transfer sigma(TDC)/sigma(DET) were measured. It shows that for different ions in an isocharged sequence, the experimental cross-section ratio sigma(DET)/sigma(SEC) varies by a factor of 3. The results confirm that the projectile core is another dominant factor besides the charge state and the collision velocity in slow (0.35-0.49v(0); v(0) denotes the Bohr velocity) highly charged ions (HCIs) with helium collisions. The experimental cross-section ratio sigma(DET)/sigma(SEC) is compared with the extended classical over-barrier model (ECBM) [A. Barany , Nucl. Instrum. Methods Phys. Res. B 9, 397 (1985)], the molecular Coulombic barrier model (MCBM) [A. Niehaus, J. Phys. B 19, 2925 (1986)], and the semiempirical scaling laws (SSL) [N. Selberg , Phys. Rev. A 54, 4127 (1996)]. It also shows that the projectile core properties affect the initial capture probabilities as well as the subsequent relaxation of the projectiles. The experimental cross-section ratio sigma(TDC)/sigma(DET) for those lower isocharged sequences is dramatically affected by the projectile core structure, while for those sufficiently highly isocharged sequences, the autoionization always dominates, hence the cross-section ratio sigma(TDC)/sigma(DET) is always small.

Single- and double-electron processes in collisions of Xe23+ ions with helium

We report the measurements of relative cross sections for single capture (SC), double capture (DC), single ionization (SI), double ionization (DI), and transfer ionization (TI) in collisions of Xe23+ ions with helium atoms in the velocity range of 0.65-1.32 a.u. The relative cross sections show a weak velocity dependence. The cross-section ratio of double-(DE) to single-electron (SE) removal from He, sigma(DE)/sigma(SE), is about 0.45. Single capture is the dominant reaction channel which is followed by transfer ionization, while only very small probabilities are found for pure ionization and double capture. The present experimental data are in satisfactory agreement with the estimations by the extended classical over-barrier (ECB) model..

Comparative molecular population genetics of phycoerythrin locus in Prochlorococcus

As the only remainder type of phycobiliproteins in Prochlorococcus, the actual role of phycoerythrin still remains unknown. Previous studies revealed that two different forms of phycoerythrin gene were found in two ecotypes of Prochlorococcus that are specifically adapted to either high light (HL) or low light (LL) conditions. Here we analyze patterns of phycoerythrin nucleotide variation in the HL- and LL-Prochlorococcus populations. Our analyses reveal a significantly greater number of non-synonymous fixed substitutions in peB and peA than expected based on interspecific comparisons. This pattern of excess non-synonymous fixed substitutions is not seen in other five phycoerythrin-related genes (peZ/V/Y/T/S). Several neutrality statistical tests indicate an excess of rare frequency polymorphisms in the LL-Prochlorococcus data, but an excess of intermediate frequency polymorphisms in the HL-Prochlorococcus data. Distributions of the positively selected sites identified using the likelihood ratio test, when mapped onto the phycoerythrin tertiary structure, reveal that HL- and LL-phycoerythrin should be under different selective patterns. These findings may provide insights into the likely role of selection at the phycoerythrin locus and motivate further research to unveil the function of phycoerythrin in Prochlorococcus.

雨生红球藻中虾青素合成相关酶基因的转录调控序列分析

虾青素是一种具有极强抗氧化活性的类胡萝卜素，具有广泛的应用价值。雨生红球藻是一种单细胞绿藻，在逆境胁迫条件下能够大量合成并迅速积累虾青素，其积累量最高可达细胞干重的4%，从而成为目前首选的天然虾青素合成工具。但是，虾青素的大量积累总是发生在不适于生物量积累的环境胁迫条件下，虾青素积累与生物量积累之间成为一对矛盾，制约着虾青素大量生产。 异戊烯焦磷酸异构酶（IPI）、β-胡萝卜素酮化酶（BKT）和β-胡萝卜素氧化酶（CRTO）是虾青素合成过程中的相关酶。已有研究结果表明，这些酶基因的表达调控至少是部分发生在转录水平上的，这就为我们从转录水平上研究虾青素生物合成关键酶基因的调控机制提供了重要线索。 本文研究结果如下： 1. 利用基因组步移的方法克隆了两条异戊烯焦磷酸异构酶基因（ipi）的5’上游侧翼序列（1.8kb和2.5kb），预示着ipi的转录由不止一个启动子调控。 2. 利用上述方法克隆了两条β-胡萝卜素氧化酶基因（crtO）5'上游侧翼序列（1kb和2kb）。以lacZ为报告基因的瞬间表达实验结果表明，长度为320bp(-682/-363)的crtO 5'上游侧翼序列具有很强的启动转录活性，提示这段序列包含了启动子的结构。 3. 利用凝胶阻滞的方法研究了雨生红球藻中bkt强启动转录活性区域，即 309bp(-617/-309)启动子区域的转录因子结合位点，并发现在-396/-338的59bp区域内存在特异的核蛋白结合位点。通过序列分析，发现此59bp区域并不包含TATA或者CAAT-box，而是存在对光、缺氧、p-香豆酸及激素反应的G-box。 4. 根据国外已经获得的ipi和crtO全长cDNA序列，利用长距离PCR法从红球藻基因组中扩增到基因组序列。发现ipi和crtO均包含6个外显子和5个内含子，内含子的剪切位点基本符合GU-AG规律。并通过似然比检验（Likelihood ratio test）的方法发现两基因在进化过程中存在着正选择现象。 这些工作为下一步继续寻找与上述特定DNA调控区域特异结合的反式作用因子（蛋白质因子）奠定了基础。

Topology of toroidal helical fields in non-circular cross-sectional tokamaks

The ordinary differential magnetic field line equations are solved numerically; the tokamak magnetic structure is studied on Hefei Tokamak-7 Upgrade (HT-7U) when the equilibrium field with a monotonic q-profile is perturbed by a helical magnetic field. We find that a single mode (m, n) helical perturbation can cause the formation of islands on rational surfaces with q = m/n and q = (m +/- 1, +/- 2, +/- 3,...)/n due to the toroidicity and plasma shape (i.e. elongation and triangularity), while there are many undestroyed magnetic surfaces called Kolmogorov-Arnold-Moser (KAM) barriers on irrational surfaces. The islands on the same rational surface do not have the same size. When the ratio between the perturbing magnetic field B-r(r) and the toroidal magnetic field amplitude B(phi)0 is large enough, the magnetic island chains on different rational surfaces will overlap and chaotic orbits appear in the overlapping area, and the magnetic field becomes stochastic. It is remarkable that the stochastic layer appears first in the plasma edge region.

Geometry parameter optimization of large cross-sectional S-shaped bent rib waveguides for silicon based optical switches

地址: Chinese Acad Sci, Inst Semicond, State Key Lab Integrated Optoelect, Beijing 100083, Peoples R China

The driving potential and cross sections for synthesizing super heavy nuclei with hot fusion

The dinuclear model of the formation mechanism of a superheavy compound nucleus assumes that when all nucleons of the projectile have been transferred in to the target nucleus the compound nucleus is formed. The nucleon transfer is determined by the driving potential. For some reaction channels, the relation between nucleon transfer and the evolution path of the neutron/proton ratio is rather complicated. In principle, both the dynamical equation and the driving potential should be a twodimensional explicit function of the neutron and proton. For the sake of simplicity we calculated the driving potential by choosing the path of the nucleon transfer which is related to the nutron/proton ratio, and the calculated evaporation residue cross-sections to synthesize the superheavy nuclei are much closer to the experimental data

Cross-correlation between WMAP and 2MASS: non-Gaussianity induced by the SZ effect

We study the non-Gaussianity induced by the Sunyaev-Zel'dovich (SZ) effect in cosmic microwave background (CMB) fluctuation maps. If a CMB map is contaminated by the SZ effect of galaxies or galaxy clusters, the CMB maps should have similar non-Gaussian features to the galaxy and cluster fields. Using the WMAP data and 2MASS galaxy catalogue, we show that the non-Gaussianity of the 2MASS galaxies is imprinted on WMAP maps. The signature of non-Gaussianity can be seen with the fourth-order cross-correlation between the wavelet variables of the WMAP maps and 2MASS clusters. The intensity of the fourth-order non-Gaussian features is found to be consistent with the contamination of the SZ effect of 2MASS galaxies. We also show that this non-Gaussianity can not be seen by the high-order autocorrelation of the WMAP. This is because the SZ signals in the autocorrelations of the WMAP data generally are weaker than the WMAP-2MASS cross-correlations by a factor f(2), which is the ratio between the powers of the SZ-effect map and the CMB fluctuations on the scale considered. Therefore, the ratio of high-order autocorrelations of CMB maps to cross-correlations of the CMB maps and galaxy field would be effective to constrain the powers of the SZ effect on various scales.

Double neutron/proton ratio of nucleon emissions in isotopic reaction systems as a robust probe of nuclear symmetry energy

The double neutron/proton ratio of nucleon emissions taken from two reaction systems using four isotopes of the same element, namely, the neutron/proton ratio in the neutron-rich system over that in the more symmetric system, has the advantage of reducing systematically the influence of the Coulomb force and the normally poor efficiencies of detecting low energy neutrons. The double ratio thus suffers less systematic errors. Within the IBUU04 transport model the double neutron/proton ratio is shown to have about the same sensitivity to the density dependence of nuclear symmetry energy as the single neutron/proton ratio in the neutron-rich system involved. The double neutron/proton ratio is therefore more useful for further constraining the symmetry energy of neutron-rich matter.

Influences of the isospin-dependence of in-medium nucleon nucleon cross-section and momentum dependent interaction on isoscaling parameter

Influences of the isospin-dependent in-medium nucleon nucleon cross-section (sigma(iso)(NN) and momentum-dependent interaction (MDI) on the isoscaling parameter a are investigated for two central collisions Ca-40 +Ca-40 and Ca-60+ Ca-60. These collisions are with isospin dependent quantum molecular dynamics in the beam energy region from 40 to 60 MeV/nucleon. The isotope yield ratio R-21 (N, Z) for the above two central collisions depends exponentially on the neutron number N and proton number Z of isotopes, with an isoscaling. In particular, the isospin-dependent (sigma(iso)(NN) and MDI induce an obvious de crease of the isoscaling parameter a. The mechanism of the decreases of a by both sigma(iso)(NN) and MDI are studied respectively.

Synthesis and characterization of photo-cross-linked hydrogels based on biodegradable polyphosphoesters and poly(ethylene glycol) copolymers

Novel biodegradable hydrogels by photo-cross-linking macromers based on polyphosphoesters and poly(ethylene glycol) (PEG) are reported. Photo-cross-linkable macromers were synthesized by ring-opening polymerization of the cyclic phosphoester monomer 2-(2-oxo-1,3,2-dioxaphospholoyloxy) ethyl methacrylate (OPEMA) using PEG as the initiator and stannous octoate as the catalyst. The macrorners were characterized by H-1 NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography measurements. The content of polyphosphoester in the macromer was controlled by varying the feed ratio of OPEMA to PEG. Hydrogels were fabricated by exposing aqueous solutions of macromers with 0.05% (w/w) photoinitiator to UV light irradiation, and their swelling kinetics as well as degradation behaviors were evaluated. The results demonstrated that cross-linking density and pH values strongly affected the degradation rates. The macromers was compatible to osteoblast cells, not exhibiting significant cytotoxicity up to 0.5 mg/mL. "Live/dead" cell staining assay also demonstrated that a large majority of the osteoblast cells remained viable after encapsulation into the hydrogel constructs, showing their potential as tissue engineering scaffolds.

Preparation of fully cross-linked CNBR/PP-g-GMA and CNBR/PP/PP-g-GMA thermoplastic elastomers and their morphology, structure and properties

Binary CNBR/PP-g-GMA and ternary CNBR/PP/PP-g-GMA thermoplastic elastomers were prepared by reactive blending carboxy nitrile rubber (CNBR) powder with nanometer dimension and polypropylene functionalized with glycidyl methacrylate (PP-g-GMA). Morphology observation by using an atomic force microscope (AFM) and TEM revealed that the size of CNBR dispersed phase in CNBR/PP-g-GMA binary blends was much smaller than that of the corresponding CNBR/PP binary blends. Thermal behavior of CNBR/PP-g-GMA and CNBR/PP blends was studied by DSC. Comparing with the plain PP-g-GMA, T, of PP-g-GMA in CNBR/PP-g-GMA blends increased about 10degreesC. Both thermodynamic and kinetic effects would influence the crystallization behavior of PP-g-GMA in CNBR/PP-g-GMA blends. At a fixed content of CNBR, the apparent viscosity of the blending system increased with increasing the content of PP-g-GMA. FTIR spectrum verified that the improvement of miscibility of CNBR and PP-g-GMA was originated from the reaction between carboxy end groups of CNBR and epoxy groups of GMA grafted onto PP molecular chains. Comparing with CNBR/PP blends, the tensile strength, stress at 100% strain, and elongation at break of CNBR/PP-g-GMA blends were greatly improved.