Biosorption behavior and mechanism of thorium on Bacillus sp. dwc-2 isolated from soil

To develop a microbe-based bioremediation strategy for cleaning up thorium-contaminated sites, we have investigated the biosorption behavior and mechanism of thorium on Bacillus sp. dwc-2, one of the dominant species of bacterial groups isolated from soils in Southwest China. Thorium biosorption depended on the p H of environment, and its rapid biosorption reached a maximum of up to 10.75 mg Th per gram of the bacteria(wet wt.) at pH 3.0. The biosorption agreed bettter with Langmuir isotherm model than Freundlich model, indicating that thorium biosorption was a monolayer adsorption. The thermodynamic parameters, negative change in Gibbs free energy and positive value in enthalpy and entropy, suggested that the biosorption was spontaneous,more favorable at higher temperature and endothermic process with an increase of entropy. Scanning electron microscopy(SEM) indicated that thorium initially binded with the cell surface, while transmission electron microscopy(TEM) revealed that Th deposited in the cytoplasm and served as cores for growth of element precipitation(e.g., phosphate minerals) or by self-precipitation of hydroxides, which is probably controlled by ion-exchange, as evidenced by particle induced X-ray emission(PIXE) and enhanced proton backscattering spectrometry(EPBS). Fourier Transform Infrared(FTIR) further indicated that thorium biosorption involved carboxyl and phosphate groups and protein in complexation or electrostatic interaction. Overall results indicated that a combined electrostatic interaction-complexation-ion exchange mechanism could be involved in thorium biosorption by Bacillus sp. dwc-2.

Phase and Rietveld Refinement of Pyrochlore Gd_2Zr_2O_7 Used for Immobilization of Pu(Ⅳ)

The phase of pyrochlore Gd_2Zr_2O_7 used for immobilization of Pu （Ⅳ） was investigated, tetravalent cerium was used as the simulacrum for plutonium with tetravalence, and the compounds in the system Gd_2Zr_2-_xCe_xO_7 （0.0≤x≤2.0） were synthesized via a high temperature solid reaction method with Gd_2O_3 and ZrO_2 powders being used as the starting materials. Based on the collected XRD data of the gained samples, the phase and microstructural change of compounds were calculated by means of rietveld structural refinement method. The experimental results indicated that the phases of compounds were changed from pyrochlore to fluorite-type phase with the increasing x. The linear relation between a and x was discovered in the range of fluorite-type phase, which accorded with a = 0.52748 ＋ 0.00825 x （0.2≤x≤2.0）, while V= 0.14668 ＋ 0.00711 x （0.2≤x≤2.0） was also achieved.

Phase and Structure in the System Gd_(2-x)Eu_xZr_2O_7 (0.0≤x≤2.0)

Pyrochlore Gd2Zr2O7 are considered as an excellent candidate for treatment of radioactive waste forms, because of its superior physical, chemical and anti-irradiation properties. To investigate the phase and structure of pyrochlore Gd2Zr2O7 used for immobilizing Pu （Ⅲ）, trivalent europium was used as the simulacrum for plutonium with trivalence. The compounds of stoichiometry Gd2-xEuxZr2O7（0.0≤x≤ 2.0） synthesized by high temperature solid state reaction method, were analyzed with the help of XRD and Rietveld structural refinement method. The results indicated that the phases of compounds continuously kept the phase of pyrochlore under our experimental condition. The linear relation between a and x was discovered in the system of Gd2-xEuxZr2O7（0.0≤x≤ 2.0） at 1 773 K, which accorded with a = 10.538 41 ＋ 0.008 95 x, V = 1 170.373 32 ＋ 2.985 97 x.

Lattice QCD Calculation of ππ Scattering Length

We study s-wave pion-pion scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV.In the "Asqtad" improved staggered fermion formulation,we measure full ππ four-point correlators for isospin I = 0 and 2 channels,and use chiral perturbation theory at next-to-leading order to extrapolate our simulation results.Extrapolating to the physical pion mass yields scattering lengths as mπaI=2 0 = 0.041 6(2) and m π a I =0 0 = 0.186(2) for isospin I = 2 and 0 channels,respectively.Our lattice simulation for ππ scattering length in I = 0 channel is an exploratory study,where we include the disconnected contribution,and our preliminary result is near to its experimental value.These simulations are carried out with MILC 2 + 1 flavor gauge configurations at lattice spacing a ≈ 0.15 fm.

Leaching Stability of Simulated Waste Forms for Immobilizing An^(3+) by Gd_2Zr_2O_7 with Nd^(3+)

In order to investigate the anti-leaching capability of pyrochlore Gd2Zr2O7 immobilized An3＋, trivalent neodymium was used as the simulacrums for radioactive wastes with trivalence, Gd2-xNdxZr2O7（0.0 ≤ x≤2.0） series samples were successfully synthesized by high temperature solid reaction and using Gd2O3, ZrO2 powders as starting materials. The experiments of long-term chemical stability were conducted in synthetic seawater at 40 and 70 ℃. The XRD diffractive data and extraction ratio of as-received samples were collected with the help of X-ray diffraction （XRD） instrument and inductively coupled plasma mass spectrometry （ICP- Mass）. The results indicate that the phases of as-received compounds keep the single phase of pyrochlore. The extraction ratio of Gd3＋, Zr4＋ and Nd3＋ in waste forms is increasing with the increase of immersion time in synthetic seawater. The extraction ratio of waste forms at 70 ℃ is higher than at 40 ℃. The highest extraction ratio of Gd3＋, Zr4＋ and Nd3＋ after 42 days is near 0.025 8, 0.003 8 and 0.045 2 μg.mL-1, respectively.

Off-axis dose distribution for rectangle proton beam

This papcr modifies an analytical algorithm originally developed for electron dose calculations to evaluate the off-axis dose distribution of rectangle proton bcam. This spatial distribution could be described by Fermi-Eyges theory since a proton undergoes small-angle scattering when it passes through medium. Predictions of the algorithm for relative off-axis dose distribution by a 6 cm ＊ 6 cm initial monoenergetic proton beam are compared with the results from the published Monte Carlo simulations. The excellent level of agreement between the results of these two methods of dose calculation （〈 2%） demonstrates that the off-axis dose distribution from rectangle proton beam may be computed with high accuracy using this algorithm. The results also prompts the necessity to consider the off-axis distribution when the proton is applied to clinical radiotherapy since the penumbra is significant at the distal of its range （about 0.6 cm at the Bragg-peak depth）.

Preliminary Lattice Study of I=0 KK Scattering

We deliver the realistic ab initio lattice investigations of KK scattering.In the Asqtad-improved staggered dynamical fermion formulation,we carefully measure KˉK four-point function in the I=0 channel by moving wall sources without gauge fixing,and clearly find an attractive interaction in this channel,which is in agreement with the theoretical predictions.An essential ingredient in our lattice calculation is to properly treat the disconnected diagram.Moreover,we explain the difculties of these lattice calculations,and discuss the way to improve the statistics.Our lattice investigations are carried out with the MILC 2+1 gauge configuration at lattice spacing a≈0.15 fm.

High temperature property studies of the 6H-SiC MOS capacitor

N-type and p-type 6H-SiC metal oxide semiconductor (MOS) capacitor samples are fabricated with a typical method,and the high frequency capacitor voltage (C-V) curves of these samples are measured at temperatures ranging from 293 to 533 K.There exists huge difference between the n-type and p-type samples.Flat-band voltage shift of the n-type sample becomes larger with temperature rising,but that of the p-type sample have very little change.This may be caused by the residual Al in the p-type oxide.Both types of the SiC samples follow the same rule of flat-band voltage changing with temperature.But their mechanisms are different as temperature is above 453 K.Of both types the p-type SiC is more suitable for high temperature applications.

Full lattice QCD study of the κ scalar meson

We studied the K light scalar meson in 2＋1 flavor full QCD with sufficiently light u and d quarks. Via lattice simulation we measured the correlators for the K channel in the ＂Asqtad＂ improved staggered fermion formulation. After chiral extrapolation we obtained the mass of the K meson with 826± 119 MeV, which is within recent experimental values of 800-900 MeV. The simulations were carried out with the MILC 2＋1 flavor gauge configurations at lattice spacing a ≈ 0.15 fm.

Bubble contributions to scalar correlators with mixed actions

Within mixed-action chiral perturbation theory （MAxPT）, Sasa＇s derivation of the bubble contribution to scalar a0 meson is extended to those of scalar K and o- mesons. We revealed that the K bubble has two double poles and the （~ bubble contains a quadratic-in-t2 growth factor stemming from the multiplication of two double poles for a general mass tuning of valence quarks and sea quarks. The corresponding preliminary analytical expressions in MAxPT with 2＋1 chiral valence quarks and 2＋1 staggered sea quarks will be helpful for lattice studies of scalar mesons.

Scalar meson spectroscopy with a fine lattice

With sufficiently light u and d quarks the isovector （a0） and isosinglet （f0） scalar meson propagators are dominated at large distances by two-meson states. In the staggered fermion formulation of lattice QCD, taste-symmetry breaking causes a proliferation of multihadron states that complicates the analysis of these channels. Of special interest is the bubble contribution, which makes a considerable contribution to these channels. Using numerical simulation we have measured the correlators for both a0 and f0 channels in the ＂Asqtad＂ improved staggered fermion formulation in a MILC fine （a = 0.09 fm） lattice ensemble. We analyze those correlators using rooted staggered chiral perturbation theory （rSxPT） and achieve chiral couplings that are well consistent with previous determinations.

I=1/2 low-lying mesons in lattice QCD

Using a conventional constituent-quark model, I = 1/2 scalar K, vector K＊（892）, and axial vector K1 mesons are studied in the asqtad-improved staggered fermion with wall-source and point-sink interpolators. The mass ratio of mK/mz＊（892） is numerically confirmed to apparently vary with quark mass, and the experimental ordering mK.（892） 〉 mK holds elegantly when the light u/d quark masses are sufficiently small, while the valence strange quark mass is fixed to its physical value. We also get reasonable signals for the K1 meson suggested by the SCALAR Collaboration from lattice QCD. The computations are conducted with the MILC Nf=3 flavor gauge configurations at three lattice spacings： a≈0.15, 0.12, and 0.09 fm.