基于“慕课”的物理类微课程设计探索

“慕课”起步,微课程先行!鉴于目前微课程设计缺乏规范模式,本文旨在对此进行深入探讨．在微课程设计缺乏充分的理论基础支持的前提下,本文首先利用文献综述法归纳得出微课程的基本特征,据此确定微课程设计原则;其次以此原则为指导,借鉴远程开放教育的设计模式,类比探索出微课程设计的基本模式;最后将这种微课程设计模式应用于物理类课程,并结合物理类课程特点进行实证分析,成功实现了物理类微课程设计．教学实践活动进一步检验了本文构建的微课程设计模式切实可行、效果良好．     

Attacks and Improvement of Quantum Sealed-Bid Auction with EPR Pairs

Recently, an experimentally feasible three-party quantum sealed-bid auction protocol based on EPR pairs [Z.Y. Wang, Commun. Theor. Phys. 54 （2010） 997] was proposed. However, this study points out Wang＇s protocol cannot resist some internal bidders＇ attacks, such as the Twiee-CNOT attack, the collusion attack. A malicious bidder can launch the Twice-CNOT attack to obtain the other＇s bid, or the dishonest auctioneer may collude with one bidder and help him/her win the action by changing his/her bid. For preventing against these attacks, a simple solution by using the QKD-based message encryption and a post-confirmation mechanism by adopting the hash function are proposed.     

Measurement of 129Xe frequency shift due to Cs–129Xe collisions

Enhancement factor K0, which characterizes NMR and EPR frequency shifts for Cs-129Xe, is measured for the first time. The enhancement factor r-o was measured to be （702±41） at 80 ℃ and （653±20） at 90 ℃, using the NMR frequency shift, detected by atomic magnetometer at a low magnetic field of 100 nT. This result is useful for predicting the EPR frequency shifts for Cs and the NMR frequency shifts for 129Xe in spin-exchange cells.     

Giant optical activity and circular dichroism in the terahertz region based on bi-layer Y-shaped chiral metamaterial

We present a bi-layer Y-shaped chiral metamaterial (CMM) that can realize a giant optical activity and circular dichroism (CD) effect to the incident linear polarization wave in the terahertz (THz) region. Numerical simulation results exhibit that the pronounced CD effect with a great difference between the transmission coefficients for the circularly polarized waves can be obtained at 5.06 THz, meanwhile the 90°-polarization rotation can be observed at 5.2 THz when a y-polarized wave is incident to this CMM propagating along the −z-axis. The mechanism of the optical activity and giant CD effect is illustrated by simulated surface current distributions. Further, the influences of the structural parameters of the proposed CMM to the optical activity and CD effect have been investigated numerically.     

A study on small-world brain functional networks altered by postherpetic neuralgia

Understanding the effect of postherpetic neuralgia (PHN) pain on brain activity is important for clinical strategies. This is the first study, to our knowledge, to relate PHN pain to small-world properties of brain functional networks. Functional magnetic resonance imaging (fMRI) was used to construct functional brain networks of the subjects during the resting state. Sixteen patients with PHN pain and 16 (8 males, 8 females for both groups) age-matched controls were studied. The PHN patients exhibited decreased local efficiency along with non-significant changes of global efficiency in comparison with the healthy controls. Moreover, regional nodal efficiency was found to be significantly affected by PHN pain in the areas related to sense (postcentral gyrus, inferior parietal gyrus and thalamus), memory/affective processes (parahippocampal gyrus) and emotional activities (putamen). Significant correlation (p < 0.05) was also found between the nodal efficiency of putamen and pain intensity in PHN patients. Our results suggest that PHN modulates the local efficiency, and the small-world properties of brain networks may have potentials to objectively evaluate pain information in clinic.     

基于三维简并四波混频的PDT光敏剂HA瞬态光栅特性研究

竹红菌甲素(hypocrellin A,HA)具有丰富的激发态特性,有可能在新型光动力疗法(PDT)光敏剂、激光染料和新型光电器件方面有一定的应用前景。利用瞬态光栅技术研究了竹红菌甲素分别在不同极性和粘度溶剂中以及溶剂本身的瞬态光栅特性,把其瞬态光栅的超快过程归结为竹红菌甲素质子转移形成的过渡态TS*的衰减,得出过渡态TS*瞬态光栅的寿命为10.5 ps。竹红菌甲素分子的质子转移过渡态TS*瞬态光栅寿命不受溶剂极性和粘度的影响。     

Electronic structure and optical properties of CdWO4 with oxygen vacancy studied from first principles

The electronic structures, dielectric functions and absorption coefficient of both perfect CdWO₄ crystal (CWO) and the CWO crystal containing oxygen vacancy (CWO: V _O) have been studied using the CASTEP code with the lattice structure optimized. The calculated total density of states (TDOS) of CWO: V _O indicates that the oxygen vacancy would introduce a new electronic state within the band gap compared with that of perfect CWO. The dielectric functions are calculated since the imaginary part of the dielectric function can reduce the optical absorption of a certain crystal, and then the absorption coefficient is calculated. The calculated absorption spectra show that CWO: V _O exhibits two absorption bands in the ultraviolet and visible region, peaking at about 3.0 eV (413 nm) and 3.5 eV (354 nm), respectively, which are in agreement with the experimental results showing that the yellow CWO has two optical absorption bands in this region peaking at around 350 nm and 400 nm respectively. It can be concluded that oxygen vacancy causes these two absorption bands. The calculations also indicate that the optical properties of CWO exhibit anisotropy, and can be explained by the anisotropy of the crystal lattice.     

Photoacoustic Doppler effect from flowing small light-absorbing particles

From the flow of a suspension of micrometer-scale carbon particles, the photoacoustic Doppler shift is observed. As predicted theoretically, the observed Doppler shift equals half of that in Doppler ultrasound and does not depend on the direction of laser illumination. This new physical phenomenon provides a basis for developing photoacoustic Doppler flowmetry, which can potentially be used for detecting fluid flow in optically scattering media and especially low-speed blood flow of relatively deep microcirculation in biological tissue.     

Effect of sintering atmosphere on Ni/PTC composites ceramics

In order to prepare lead-free BaTiO₃-based PTC (positive temperature coefficient) with low room temperature resistivity, metal Ni is added to BaTiO₃-based PTC samples that contain 5, 8, 10, 12, 15, 20 wt% of Ni. The sintering temperature is from 1240 °C to 1260 °C. The sintering atmosphere of Ni/PTC composites ceramics was studied. Two sintering atmospheres were adopted in this experiment; full reducing sintering atmosphere and part reducing sintering atmosphere. Controlling the dose of graphite powder can make these two reducing atmospheres. The experiment data show that the optimal sintering atmosphere is a part-reducing atmosphere. Under on the conditions mentioned above, the room temperature resistivity of the samples can drop to under 10 Ω cm and the PTC jump can reach 10³, which represents a good PTC characteristic.     

Microwave-assisted synthesis of SrFe12O19 hexaferrites

Ultra-fine and homogeneous SrFe₁₂O₁₉ hexaferrites were synthesized by a microwave-assisted calcination route. The calcined precursors were prepared by a sol-gel auto-combustion method using Fe(NO₃)₃·9H₂O, Sr(NO₃)₂ and citric acid as starting materials. The structures, powder morphology and magnetic properties of the products were characterized by X-ray diffraction, scanning electron microscope and vibrating sample magnetometer. The results showed that microwaves are helpful to reduce the calcination temperature and shorten the calcination time. The ferrites with saturation magnetization, remanence and intrinsic coercivity of 54.80 emu/g, 29.52 emu/g and 5261 Oe, respectively, were obtained in samples calcined at 800 °C for 80 min.