[en] The usual procedure using free-atom/ion wave functions to calibrate the Moessbauer isomer shifts is modified in order to include solid state and band structure effects properly. To estimate the electron densities at the nucleus, self-consistent-field Dirac-Fock-Slater wave functions are calculated for several electronic configurations of germanium atoms and ions, taking into account the finite space allowed to these atoms (ions) in solids. Using experimental isomer shift (IS) values, the calibration constants for ⁷³Ge both for the 67.03 and 13.3 keV transitions are calculated, giving the relative change of the nuclear-charge radius ΔR/R = 0.5 x 10^-3 and ΔR/R = 1.2 x 10^-3, respectively. The accuracy of the calibration procedure is discussed. (author)

[en] We report a theoretical investigation of the spatial self-phase modulation (SSPM) effect and nonlinear ellipse rotation of both hybridly polarized vector beams and elliptically polarized vector beams through isotropic Kerr nonlinearities. It is demonstrated that the SSPM intensity pattern, the distribution of state of polarization, and the spin angular momentum (SAM) flux of a hybridly polarized vector beam could be manipulated by tuning the magnitude of the isotropic optical nonlinearity. Interestingly, we observed the radial-variant nonlinear ellipse rotation of elliptically polarized vector beams through isotropic Kerr nonlinearities. Our results may find interesting applications in nonlinear mechanism analysis, nonlinear characterization technique, and SAM manipulation. (paper)

[en] Microwave vacuum devices are used in a wide variety of areas, such as radar, space technology, electron accelerators, free electron lasers. The cathodes, i.e. the electron sources, are the cores of high-power microwave sources. Their performances directly determine the output power, lifetime and other properties of the microwave sources. It is necessary to know the actual temperature of a thermionic cathode. The temperatures of an impregnated cathode, a coated cathode and a cathode side (molybdenum tube) have been tested by infrared thermometer, optical pyrometer and thermocouple thermometer (platinum and rhodium-platinum).The results show that the temperature of an impregnated cathode tested by infrared thermometer and optical pyrometer is similar to that by thermocouple thermometer, so the temperatures of impregnated cathode tested by infrared thermometer and optical pyrometer are very close to the actual temperature by thermocouple thermometer. The temperatures of coated cathode tested by infrared thermometer and optical pyrometer are lower than the actual temperature of the cathode tested by thermocouple thermometer about 50 ℃. The temperatures of the cathode side (molybdenum tube) tested by infrared thermometer and optical pyrometer are lower than the actual temperature of the cathode by thermocouple thermometer about 60 ℃. Since the physical and chemical changes arise on the cathode surface, the temperatures of the cathode surface tested by infrared thermometer and optical pyrometer increase about 30 ℃ heated at about 1150 ℃ within 100 min. These results will be affected by the molybdenum processing technology on the surface of the material, coating material, thickness of the film, the film density and other factors. Infrared thermometer and optical pyrometer are strongly dependent on the thermal radiation coefficient of the test surface, and it is very difficult to accurately obtain the thermal radiation coefficient of some materials. (authors)

[en] This paper describes an approximate approach to quantum dynamics based on the quantum trajectory formulation of the Schrödinger equation. The quantum-mechanical effects are incorporated through the quantum potential of the mean-field type, acting on a trajectory ensemble in addition to the classical potential. Efficiency for large systems is achieved by using the quantum corrections for selected degrees of freedom and introduction of empirical friction into the ground-state energy calculations. The classical potential, if needed, can be computed on-the-fly using the Density Functional Tight Binding method of electronic structure merged with the quantum trajectory dynamics code. The approach is practical for a few hundred atoms. Applications include a study of adsorption of quantum hydrogen colliding with the graphene model, C_3_7H_1_5 and a calculation of the ground state of solid "4He simulated by a cell 180-atoms

[en] Optical trapping techniques have been of great interest and have advantages that enable the direct handling of nanoparticles. However, stable trapping of low-refractive-index nanoparticle remains challenging because the conventional two-dimensional hollow beams are only capable of trapping nanoparticle in the transverse plane. In this work, we propose a novel strategy to optically trap low-refractive-index nanoparticle in three-dimensional space with a hollow dark spherical focal spot, which is generated by 4Pi focusing of radially polarized first-order Laguerre–Gaussian beam. With the assumption that the laser power is 100 mW, the nanoparticles can be stably trapped with the maximal optical force of 0.3 pN, potential depth of 10 K _B T and stiffness of 80 pN/μm. Moreover, both the number and the position of the focal spot can be controlled by modulating the focusing condition and the gradient phase of the illumination respectively, enabling the simultaneously trapping of multiple nanoparticles with complex motion trajectory. The technique demonstrated in this work may open up new avenues for optical manipulation and their applications in various scientific fields. (paper)

[en] Similarity of equations of motion for the classical and quantum trajectories is used to introduce a friction term dependent on the wavefunction phase into the time-dependent Schrödinger equation. The term describes irreversible energy loss by the quantum system. The force of friction is proportional to the velocity of a quantum trajectory. The resulting Schrödinger equation is nonlinear, conserves wavefunction normalization, and evolves an arbitrary wavefunction into the ground state of the system (of appropriate symmetry if applicable). Decrease in energy is proportional to the average kinetic energy of the quantum trajectory ensemble. Dynamics in the high friction regime is suitable for simple models of reactions proceeding with energy transfer from the system to the environment. Examples of dynamics are given for single and symmetric and asymmetric double well potentials.

[en] The spectroscopic methods of circular dichroism (CD) is commonly used in analysing the chirality of molecules, which plays an important role in pharmaceutical compounds. However, the current methods require high sample density due to the weak CD effect of natural material, making it challenging to detect the signal of individual chiral molecule. In this work, we propose a technique to enhance CD signal of individual chiral molecule with the use of superchiral optical field, which is acquired by focusing a twisted radially polarized vortex onto a one-dimensional photonic band gap structure. Through adjusting the topological charge and the focusing angle of the illumination, a deep subwavelength optical field with full width at half maxima (FWHM) of 0.02λ and 22.4-fold superchirality factor enhancement can be generated. In addition, we demonstrate that up to 20-fold CD enhancement can be obtained by introducing 2 nm on-resonant chiral molecule into the superchiral optical field. This finding will have widely potential applications in CD spectroscopy and superresolution imaging for sparse subdiffraction chiral objects. (paper)

[en] In the ultraviolet detection system, the Si-based photodetector could be sensitised with different kinds of fluorescent material to enhance its response in the short-wavelength range. Thick-shell ZnCdS:Mn/ZnS core/shell quantum dots (QDs) exhibit unique advantages in UV signal sensitisation due to their long PL lifetime, as well as stable emission matched with CCD’s response. Herein, a single-channel UV panoramic detection system based on these Mn-doped QDs has been proposed. The QDs@PMMA film was attached on a Si-based CCD camera versus a tapered fibre, and an optical chopper was mounted before the QDs@PMMA film. The long lifetime fluorescence originating from UV signal could be still collected by the CCD camera when the chopper is in the ‘off’ state, hence the UV/vis signal ratio is significantly enhanced. (paper)

[en] We make a gradient correction to a new local density approximation form of positron–electron correlation. The positron lifetimes and affinities are then probed by using these two approximation forms based on three electronic-structure calculation methods, including the full-potential linearized augmented plane wave (FLAPW) plus local orbitals approach, the atomic superposition (ATSUP) approach, and the projector augmented wave (PAW) approach. The differences between calculated lifetimes using the FLAPW and ATSUP methods are clearly interpreted in the view of positron and electron transfers. We further find that a well-implemented PAW method can give near-perfect agreement on both the positron lifetimes and affinities with the FLAPW method, and the competitiveness of the ATSUP method against the FLAPW/PAW method is reduced within the best calculations. By comparing with the experimental data, the new introduced gradient corrected correlation form is proved to be competitive for positron lifetime and affinity calculations. (paper)

[en] To establish a gene delivery system for brain targeting, a low molecular weight polyethylenimine (PEI_10K) was modified with myristic acid (MC), and complexed with DNA, yielding MC-PEI_10K/DNA nanoparticles successfully. The nanoparticles were observed to be successfully taken up by the brains of mice. The transfection efficiency of the nanoparticles was then investigated, and both the in vitro and in vivo gene expression of MC-PEI_10K/DNA nanoparticles is significantly higher than that of unmodified PEI_10K/DNA nanoparticles. The anti-glioblastoma effect of MC-PEI_10K/pORF-hTRAIL was demonstrated by the survival time of intracranial U87 glioblastoma-bearing mice. The median survival time of the MC-PEI_10K/pORF-hTRAIL group (28 days) was significantly longer than that of the PEI_10K/pORF-hTRAIL group (24 days), the MC-PEI_10K/pGL₃ group (21 days) and the saline group (22 days). Therefore, our results suggested that MC-PEI_10K could be potentially used for brain-targeted gene delivery and in the treatment of glioblastoma.