Effective electromagnetic and chiral parameters of chiral composite material

The effective parameters of chiral composite are studied using a simple model, that is, randomly oriented non-interacting wire helices embedded in a nonchiral host medium. It is found that both the effective permittivity and permeability are independent on the handedness of the chiral objects while the effective chirality admittance is dependent. It is also found that when the ratio of the radius of the chiral helix to its pitch is about 0.23, maximum chirality admittance is achieved. The effective parameters of equichiral sample are also discussed.     

Trapping of helium atom by vacancy in tungsten: a density functional theory study

The interaction between helium (He) atom and vacancy defect in tungsten (W) has been investigated by using first-principles simulations. We have obtained that the most stable site for He in tungsten is the substitutional position because He can keep its own electronic structure at this position. In the studied tungsten system, vacancy can act as a trapping center for surrounding He atom with negative trapping energy. The migration behaviors of He atom at tetrahedral interstitial site in W, which can be trapped by vacancy but the final position is almost unchanged comparing with its initial position through structural relaxation, have been predicted and discussed. It is also found that single He atom prefers to go through an octahedral site rather than through a direct path to the vacancy, and the stronger the interaction between He atom and vacancy is, the lower the migration barrier will be.     

A new method for information retrieval in two-dimensional grating-based X-ray phase contrast imaging

Grating-based X-ray phase contrast imaging has been demonstrated to be an extremely powerful phase-sensitive imaging technique.By using two-dimensional(2D) gratings,the observable contrast is extended to two refraction directions.Recently,we have developed a novel reverse-projection(RP) method,which is capable of retrieving the object information efficiently with one-dimensional(1D) grating-based phase contrast imaging.In this contribution,we present its extension to the 2D grating-based X-ray phase contrast imaging,named the two-dimensional reverseprojection(2D-RP) method,for information retrieval.The method takes into account the nonlinear contributions of two refraction directions and allows the retrieval of the absorption,the horizontal and the vertical refraction images.The obtained information can be used for the reconstruction of the three-dimensional phase gradient field,and for an improved phase map retrieval and reconstruction.Numerical experiments are carried out,and the results confirm the validity of the 2D-RP method.     

工科物理实验课程改革与实践

针对21世纪实验教学的要求,介绍了开展工科物理实验教学体系与教学内容改革的经验。     

Ultra-low on-resistance high voltage (>600 V) SOI MOSFET with a reduced cell pitch

A low specific on-resistance (R S,on) silicon-on-insulator (SOI) trench MOSFET (metal-oxide-semiconductor-field-effect-transistor) with a reduced cell pitch is proposed.The lateral MOSFET features multiple trenches:two oxide trenches in the drift region and a trench gate extended to the buried oxide (BOX) (SOI MT MOSFET).Firstly,the oxide trenches increase the average electric field strength along the x direction due to lower permittivity of oxide compared with that of Si;secondly,the oxide trenches cause multiple-directional depletion,which improves the electric field distribution and enhances the reduced surface field (RESURF) effect in the SOI layer.Both of them result in a high breakdown voltage (BV).Thirdly,the oxide trenches cause the drift region to be folded in the vertical direction,leading to a shortened cell pitch and a reduced R S,on.Fourthly,the trench gate extended to the BOX further reduces R S,on,owing to the electron accumulation layer.The BV of the MT MOSFET increases from 309 V for a conventional SOI lateral double diffused metal-oxide semiconductor (LDMOS) to 632 V at the same half cell pitch of 21.5 μm,and R S,on decreases from 419 m · cm 2 to 36.6 m · cm 2.The proposed structure can also help to dramatically reduce the cell pitch at the same breakdown voltage.     

血清中Mo、Se、Mn、Cu、Zn与食管癌的关系探讨

通过对１８例食管癌患者以及８０例对照组血清中Ｍｏ、Ｓｅ、Ｍｎ、Ｃｕ、Ｚｎ的测定分析，发现食管瘤患者血硒含量明显低于对照组，二者之间有极显著性差异（Ｐ＜０．０１）。而血铜、铜／锌比值食管癌组明显高于对照组，差异有显著性（Ｐ＜０．０５）。Ｍｏ、Ｍｎ、Ｚｎ元素的含量在二组之间无显著性差异（Ｐ＞０．０５）．提示血清硒铜与食管癌有关。     

Image displacement based on phase-encoded reference joint fractional transform correlator

In order to utilize the space of an input plane efficiently and make the optical structure more flexible, an image displacement measurement based on phase-encoded reference joint fractional transform correlator (PER-JFrTC) is proposed. We use a random phase mask to encode the reference image and overlay it with the target image forming the input image. Joint power spectrum (JPS) of the input image is obtained by Fourier transform and the resultant is encoded by the same phase mask. Then a fractional Fourier transform with an order p is applied to the phase-encoded JPS (PJPS), resulting in a correlation output with a sharp cross-correlation peak, which includes the displacement information between the reference and the target image. Contrast to displacement measurement based on traditional joint transform correlator (JTC), PER-JFrTC can use the space of the input plane efficiently and reduces the influence of the auto-correlation. Also the position of cross-correlation peak can be fixed arbitrarily according to the fractional order p as well as the optical set-up can be more flexible and easier to implement. Results based on digital computation show that PER-JFrTC could detect the displacement accurately and verify our proposal. A possible optical set-up is suggested.     

基于壁面主动变形的湍流减阻控制研究

采用谱方法, 对反向控制下壁面主动变形的槽道湍流进行了直接数值模 拟研究. 结果表明, 在壁面最大变形量小于5倍黏性尺度条件下, 压差阻力可略, 摩擦阻力 降低7.6%. 施加控制后, 湍流强度和雷诺应力受到明显抑制, 平均速度剖面对数区上移. 受壁面法向运动的影响, 条带结构强度减弱、尺度变大; 流向涡外移且强度减弱, 其倾斜和 抬起的角度均有不同程度的减小. 壁面变形呈现流向拉长的凹槽结构, 其平均间距 为90倍黏性尺度.     

Er:SGB晶体主轴折射率测量

根据Er:Sr3Gd(BO3)3(Er:SGB)的透过率曲线粗略估计了该晶体的折射率,再利用自准直法,精确测量了30~170℃范围内,0.4880μm、0.6328μm、1.0640μm、1.338μm等波长下Er:SGB晶体的主轴折射率,得到Sellm e ier方程并计算了1.319μm下Er:SGB晶体的主轴折射率,与实验测量的结果进行比较,两者的差异不大于2×10-4,处在测量误差的范围内,验证了实验结果的可靠性。     

Harmonic Mode-Locked Er-Doped Fiber Laser Based on a Microfiber-Based PbS Nanoparticle Saturable Absorber

Lead sulfide (PbS) is a nanomaterial with excellent optical and chemical properties, such as a narrow bandgap (0.37 eV), high thermal damage threshold, and high stability. Obviously, it is appropriate as a saturable absorber (SA) device for ultrafast photonics. However, PbS nanoparticles (NPs) as the SA of ultrashort harmonic mode-locked pulse still haven't been demonstrated at present. In this paper, the PbS NPs are made into an SA-device-based microfiber by optical deposition method and connected in an integrated Erbium-doped fiber laser. And both characteristics and nonlinear optical properties of PbS NPs have been systemically investigated. A fundamental frequency mode-locked pulsed laser is proposed, whose central wavelength is 1560 nm, and the pulse width is 1 ps. In addition, high repetition rate operations are achieved, with a maximum repetition rate of 833 MHz. This is the first time that PbS NPs are used to generate 96th-order harmonic mode-locking, and the corresponding pulse duration is 987 fs. It is demonstrated that PbS NPs are a kind of SA photonic material with excellent performance. It can improve the communication capacity by applying fiber communication, and it has potential application value even in material processing and optical comb.