Kinetics of photoinduced anisotropy in bacteriorhodopsin film under two pumping beams

Photoinduced anisotropy in bacteriorhodopsin (BR) film arises from the selective bleaching of BR molecules to linearly polarized light. The kinetics of photoinduced anisotropy excited by single and two pumping beams are investigated theoretically and experimentally. Compared with a single pumping beam (650 nm), which produces comparatively small photoinduced anisotropy, dual-wavelength linearly polarized pumping beams (650 and 405 nm) can obviously change the photoinduced anisotropy. When the polarization orientation of the 405 ran pumping beam is perpendicular to that of the 650 nm pumping beam, the peak and steady values of the photoinduced anisotropy kinetic curves are remarkably enhanced. But when the two pumping beams have parallel polarization orientation, the peak and steady values are restrained. At a fixed intensity of the 650 nm pumping beam, there exists an optimal intensity for the 405 nm pumping beam to maximize the value of the photoinduced anisotropy. The photoinduced transmittance of the polarizer-BR-analyzer system is modulated by the polarization angle of the 405 nm pumping beam in an approximate-cosine form. (C) 2008 Optical Society of America.

STUDY ON PREPARATION OF GAN AND COSI2 EPITAXIAL-FILMS BY MASS ANALYZED LOW-ENERGY DUAL ION-BEAM EPITAXY

The Mass Analyzed Low Energy Dual Ion Beam Epitaxy (MALE-DIBE) system has been designed and constructed in our laboratory. We believe that the system, which was installed and came into full operation in 1988, is the first facility of this kind. With our system we have carried out studies, for the first time, on compound synthesis of GaN and CoSi2 epitaxial thin films. RHEED and AES results show that GaN films, which were deposited on Si and sapphire substrates, are monocrystalline and of good stoichiometry. To our knowledge, GaN film heteroepitaxially grown on Si. which is more lattice-mismatched than GaN on sapphire, has not been reported before by other authors. RBS and TEM investigations indicated a rather good crystallinity of CoSi2 with a distinct interface between CoSi2 and the Si substrate. The channelling minimum yield chi(min) from the Co profile is approximately 4%. The results showed that the DIBE system with simultaneous arrival of two beams at the target is particularly useful in the formation of novel compounds at a relatively low substrate temperature.

CONSTRUCTION AND APPLICATIONS OF A DUAL MASS-SELECTED LOW-ENERGY ION-BEAM SYSTEM

A direct ion beam deposition system designed for heteroepitaxy at a low substrate temperature and for the growth of metastable compounds has been constructed and tested. The system consists of two mass-resolved low-energy ion beams which merge at the target with an incident energy range 50-25 000 eV. Each ion beam uses a Freeman ion source for ion production and a magnetic sector for mass filtering. While a magnetic quadrupole lens is used in one beam for ion optics, an electrostatic quadrupole lens focuses the other beam. Both focusing approaches provide a current density more than 100-mu-A/cm2, although the magnetic quadrupole gives a better performance for ion energies below 200 eV. The typical current of each beam reaches more than 0.3 mA at 100 eV, with a ribbon beam of about 0.3-0.5 x 2 cm2. The target is housed in an ultrahigh vacuum chamber with a base pressure of 1 x 10(-7) Pa and a typical pressure of 5 x 10(-6) Pa when a noncondensable beam like argon is brought into the chamber. During deposition, the target can be heated to 800-degrees-C and scanned mechanically with an electronic scanning control unit. The dual beam system has been used to grow GaN using a Ga+ and a N+ beam, and to study the oxygen and hydrogen ion beam bombardment effects during carbon ion beam deposition. The results showed that the simultaneous arrival of two beams at the target is particularly useful in compound formation and in elucidation of growth mechanisms.

Damage assessment and preservation of suspending system of Yongle-Big-Bell

The Yongle-Big-Bell is an exquisite heritage of ancient China and has more than 600 years history. The long history renders the suspending wooden rack serious damage. Therefore, the security is of our great concern. In order to know if the wooden rack is safe or not for the conventional striking in the festival service, a systemic research work has been done. At first the existing deformation and response to the strike of the beetle were measured, and then calculations using method of material mechanics and finite element analysis were conducted. Based on the results of our research, some concluding remarks and suggestion were given: The Yongle-Big-Bell can be struck regularly without urgent danger of collapse. In view of the existence of serious rotten damage, the repair and protection of wooden rack are pressing.

HIRFL-CSR commissioning in 2006 and 2007

HIRFL-CSR, a new heavy ion cooler-storage-ring system at IMP, had been in commissioning since the beginning of 2006. In the two years of 2006 and 2007 the CSR commissioning was finished, including the stripping injection (STI), electron-cooling with hollow electron beam, C-beam stacking with the combination of STI and e-cooling, the wide energy-range synchrotron ramping from 7 MeV/u to 1000 MeV/u by changing the RF harmonic-number at mid-energy, the multiple multi-turn injection (MMI), the beam accumulation with MMI and e-cooling for heavy-ion beams of Ar, Kr and Xe, the fast extraction from CSRm and single-turn injection to CSRe, beam stacking in CSRe and the RIBs mass-spectrometer test with the isochronous mode in CSRe by using the time-of-flight method.

Radiosensitivity of hepatoma cell lines and human normal liver cell lines exposed in vitro to carbon ions and argon ions at the HIRFL

Human hepatoma (SMMC-7721) and normal liver (L02) cells were irradiated with c-rays, 12C6+ and 36Ar18+ ion beams at the Heavy Ion Research Facility in Lanzhou (HIRFL). By using the Calyculin-A induced premature chromosome condensation technique, chromatid-type breaks and isochromatid-type breaks were scored separately. Tumor cells irradiated with heavy ions produced a majority of isochromatid break, while chromatid breaks were dominant when cells were exposed to c-rays. The relative biological effectiveness (RBE) for irradiation-induced chromatid breaks were 3.6 for L02 and 3.5 for SMMC-7721 cell lines at the LET peak of 96 keVlm 1 12C6+ ions, and 2.9 for both of the two cell lines of 512 keVlm 1 36Ar18+ ions. It suggested that the RBE of isochromatid-type breaks was pretty high when high-LET radiations were induced. Thus we concluded that the high production of isochromatid-type breaks, induced by the densely ionizing track structure, could be regarded as a signature of high-LET radiation exposure.

An introduction to the trapping of clusters with ion traps and electrostatic storage devices

This paper presents an introduction to the application of ion traps and storage devices for cluster physics. Some experiments involving cluster ions in trapping devices such as Penning traps, Paul traps, quadrupole or multipole linear traps are briefly discussed. Electrostatic ion storage rings and traps which allow for the storage of fast ion beams without mass limitation are presented as well. We also report on the recently developed mini-ring, a compact electrostatic ion storage ring for cluster, molecular and biomolecular ion studies.

Linear energy transfer dependence of the effects of carbon ion beams on adventitious shoot regeneration from in vitro leaf explants of Saintpaulia ionahta

Purpose: To determine the effects of carbon ion beams with five different linear energy transfer (LET) values on adventitious shoots from in vitro leaf explants of Saintpaulia ionahta Mauve cultivar with regard to tissue increase, shoots differentiation and morphology changes in the shoots. Materials and methods: In vitro leaf explant samples were irradiated with carbon ion beams with LET values in the range of 31 similar to 151 keV/mu m or 8 MeV of X-rays (LET 0.2 keV/mu m) at different doses. Fresh weight increase, surviving fraction and percentage of the explants with regenerated malformed shoots in all the irradiated leaf explants were statistically analysed. Results: The fresh weight increase (FWI) and surviving fraction (SF) decreased dramatically with increasing LET at the same doses. In addition, malformed shoots, including curliness, carnification, nicks and chlorophyll deficiency, occurred in both carbon ion beam and X-ray irradiations. The induction frequency with the former, however, was far more than that with the X-rays. Conclusions: This work demonstrated the LET dependence of the relative biological effectiveness (RBE) of tissue culture of Saintpaulia ionahta according to 50% FWI and 50% SF. After irradiating leaf explants with 5 Gy of a 221 MeV carbon ion beam having a LET value of 96 keV/mu m throughout the sample, a chlorophyll-deficient (CD) mutant, which could transmit the character of chlorophyll deficiency to its progeny through three continuous tissue culture cycles, and plantlets with other malformations were obtained.