[en] Objective: To discuss the application of CT multiplanar reformation (CTMPR) technique in making preoperative evaluation of stent implantation therapy for malignant colonic obstruction. Methods: The clinical data of a total of 50 patients with malignant colonic obstruction who received stent implantation therapy were retrospectively analyzed. Combined with the characteristics of CTMPR technique, the value of CTMPR technique in stent implantation was assessed. Results: Depending on the related information provided by CTMPR imaging, higher success rate of colonic stent implantation was obtained. The short-term curative effect was satisfactory, and the colonic obstruction was relieved within 24 hours after stent implantation therapy in most patients. Conclusion: CTMPR imaging can provide comprehensive and useful data for colon stent implantation, which can ensure the successful management of colonic stent implantation, thereby, the success rate of stent implantation can be well improved. (authors)

[en] Precision measurement of the 4s"2S_1_/_2–3d"2D_5_/_2 clock transition based on "4"0Ca"+ ion at 729 nm is reported. A single "4"0Ca"+ ion is trapped and laser-cooled in a ring Paul trap, and the storage time for the ion is more than one month. The linewidth of a 729 nm laser is reduced to about 1 Hz by locking to a super cavity for longer than one month uninterruptedly. The overall systematic uncertainty of the clock transition is evaluated to be better than 6.5×10"−"1"6. The absolute frequency of the clock transition is measured at the 10"−"1"5 level by using an optical frequency comb referenced to a hydrogen maser which is calibrated to the SI second through the global positioning system (GPS). The frequency value is 411 042 129 776 393.0(1.6) Hz with the correction of the systematic shifts. In order to carry out the comparison of two "4"0Ca"+ optical frequency standards, another similar "4"0Ca"+ optical frequency standard is constructed. Two optical frequency standards exhibit stabilities of 1×10"−"1"4τ"−"1"/"2 with 3 days of averaging. Moreover, two additional precision measurements based on the single trapped "4"0Ca"+ ion are carried out. One is the 3d"2D_5_/_2 state lifetime measurement, and our result of 1174(10) ms agrees well with the results reported in [Phys. Rev. A 62 032503 (2000)] and [Phys. Rev. A 71 032504 (2005)]. The other one is magic wavelengths for the 4s"2S_1_/_2–3d"2D_5_/_2 clock transition; λ_|_m__j_|_=_1_/_2= 395.7992(7) nm and λ_|_m__j__|_=_3_/_2 = 395.7990(7) nm are reported, and it is the first time that two magic wavelengths for the "4"0Ca"+ clock-transition have been reported. (topical review)

[en] Frequency comparison is one of the most efficient ways to evaluate the performance of a frequency standard. Based on the pre-existing "4"0Ca"+ optical frequency standard, we set up the second "4"0Ca"+ optical frequency standard, which has been improved in the materials and structure of ion traps for better control of the magnetic field. After the compensation, the residual magnetic field at the position of the ion is adjusted to be ∼500 nT with a long time jitter of ∼10nT, which is better than the pre-existing "4"0Ca"+ optical frequency standard. We realize the ‘4-point-closed-loop locking’ on the second "4"0Ca"+ optical frequency standard after a series of preparatory works. Through half an hour of measurement time, the two frequency standards exhibited a stability of 2.1 × 10"−"1"3 τ "−"1"/"2 and a relative frequency difference of 1.5 (2.9) Hz

[en] We observed the linear-to-zigzag structural phase transition of a ⁴⁰Ca+ crystal in a homemade linear Paul trap. The values of the total temperature of the ion crystals during the phase transition are derived using the molecular-dynamics (MD) simulation method. A series of simulations revealed that the ratio of the radial to axial secular frequencies has a dependence on the total temperature that obeys different functional forms for linear and zigzag structures, and the transition point occurs where these functions intersect; thus, the critical value of the ratio of secular frequencies that drives the structure phase transition can be derived. (atomic and molecular physics)