[en] Due to the high symmetry of the icosahedron, many of the electronic and vibrational levels of the C₆₀ molecule and its rela.ted compounds are highly degenerate. Therefore in dealing with properties of the C₆₀ and the related compounds, the Jahn-Teller (JT) interaction must be considered. The C₆₀ molecule is known to exhibit a strong electron-phonon interaction. Hence studies of the Jahn-Teller (JT) effect are important in understanding the properties of C₆₀ and related molecules. Many kinds of JT effects are possible in icosahedral symmetry which the C₆₀ molecule possesses. The high degeneracies that occur in this symmetry generate problems which are not seen in cubic systems, such as the JT G x (g + h) and H x (g + h) systems. Depending on the ratio of the vibronic coupling constants, the wells on the lowest adiabatic potential energy surface (APES) for the G x (g + h) JT system, are of T or D₃ symmetry; for the H x (g + h) JT system, the wells on the lowest APES are of D_5d or D_3d symmetry. For the case of D_3d minima in the simpler H x h JT system, it has previously been found unexpectedly that, above a certain coupling strength, the A-type level has a lower energy than the H-state. This is the first known example of a linear JT system in which the JT effect effectively alters the symmetry of the ground state. However, a physical explanation of why this crossover occurs deserves further consideration. In this thesis, an explanation based on the competition between the two tunneling paths on the lowest APES is proposed. It is assumed that tunneling occurs along paths of steepest descent. The reversal in sign of the tunneling splitting, calculated using the WKB method, in the icosahedral H x h Jahn-Teller system is explained in terms of different tunneling paths along which the system moves as the strength of the vibronic coupling K_h1 changes. It is found that this sign reversal occurs when K_h1/(h/2π)w ∼ 4.1. This result is very near to the original result of K_h1/(h/2π)w ∼ 3.8 obtained using a totally different method. This reversal can be explained as follows; for weak vibronic coupling, the H symmetry state is dominated by tunneling along the steepest descent path of C₁ symmetry which connects two D_3d wells via one point on the D₃ symmetry saddle trough; for strong coupling, the A symmetry state is dominated by tunneling along the steepest descent path of C₂ symmetry winch connects two different D_3d wells via a point on a saddle trough of T symmetry. Reduction factors (RFs) are needed when modeling vibronic systems by an effective Hamiltonian in an electronic basis. The results of analytical calculations of the second-order RFs are presented in this thesis for the ground states of the icosahedral G x (g + h) and H x (g + h) JT systems in analyticaI form. These second-order RFs are calculated for the isotropic case using simple excited states in the wells. Details are given for the G x g JT system from wells of T symmetry, for the G x h JT system from wells of D_3d symmetry and for the G x (g + h) JT system for wells of D_3D symmetry. Also, second order RFs for the H x g JT system for wells of D_3d symmetry, for the H x h₁ JT system for wells of D_3d symmetry and for the H x h₂ JT system for wells of D_5d symmetry. These results are particularly useful in investigations of the vibronic coupling effects in C₆₀ molecules. (author)

[en] This paper studies a solid film lying on a liquid layer, which in turn lies on a solid substrate. It is well known that, subject to a compressive membrane force, the solid film wrinkles, dragging the liquid underneath to flow. When the solid film is very thin, the ratio between the number of atoms at the surface and that in the bulk becomes significant, so that surface stress contributes to the membrane force. When the liquid layer is very thin, the two interfaces bounding the liquid interact with each other through forces of various physical origins. We formulate the free energy of the system, and carry out a linear perturbation analysis. A dimensionless parameter is identified to quantify the relative importance of flexural rigidity, membrane force, and interfacial force on stability of the structure. Depending on the nature of the interfacial force, several intriguing behaviors are possible; for example, the solid film may remain flat under a compressive membrane force, or form wrinkles under a tensile membrane force. We estimate the dimensionless parameter for interfacial forces of several specific origins, including photon dispersion, electrical double layer, and electron confinement. Emphasis is placed on identifying the thickness ranges of the solid film and of the liquid layer within which these forces are important

[en] Recently, the theoretical prediction on carrier mobility of two-dimensional (2D) materials has aroused wild attention. At present, there is still a large gap between the theoretical prediction and the device performance of the semiconductor based on the 2D layer semiconductor materials such as graphene. It is particularly important to theoretically design and screen the high-performance 2D layered semiconductor materials with suitable band gap and high carrier mobility. This paper introduces some 2D materials with fine properties and deduces the formula for mobility of the isotropic materials on the basis of the deformation potential theory and Fermic golden rule under acoustic phonon scattering conditions, and then discusses the carrier mobility of anisotropic materials with Dirac cones. We point out the misconceptions in the existing literature and discuss the correct ones. (paper)

[en] To investigate the sources and formation mechanisms of carbonaceous aerosols, a major contributor to severe particulate air pollution, radiocarbon (14C) measurements were conducted on aerosols sampled from November 2015 to November 2016 in Xi'an, China. Based on the 14C content in elemental carbon (EC), organic carbon (OC) and water-insoluble OC (WIOC), contributions of major sources to carbonaceous aerosols are estimated over a whole seasonal cycle: primary and secondary fossil sources, primary biomass burning, and other non-fossil carbon formed mainly from secondary processes. Primary fossil sources of EC were further sub-divided into coal and liquid fossil fuel combustion by complementing 14C data with stable carbon isotopic signatures. The dominant EC source was liquid fossil fuel combustion (i.e., vehicle emissions), accounting for 64 % (median; 45 %–74 %, interquartile range) of EC in autumn, 60 % (41 %–72 %) in summer, 53 % (33 %–69 %) in spring and 46 % (29 %–59 %) in winter. An increased contribution from biomass burning to EC was observed in winter (∼28 %) compared to other seasons (warm period; ∼15 %). In winter, coal combustion (∼25 %) and biomass burning equally contributed to EC, whereas in the warm period, coal combustion accounted for a larger fraction of EC than biomass burning. The relative contribution of fossil sources to OC was consistently lower than that to EC, with an annual average of 47±4 %. Non-fossil OC of secondary origin was an important contributor to total OC (35±4 %) and accounted for more than half of non-fossil OC (67±6 %) throughout the year. Secondary fossil OC (SOCfossil) concentrations were higher than primary fossil OC (POCfossil) concentrations in winter but lower than POCfossil in the warm period. Fossil WIOC and water-soluble OC (WSOC) have been widely used as proxies for POCfossil and SOCfossil, respectively. This assumption was evaluated by (1) comparing their mass concentrations with POCfossil and SOCfossil and (2) comparing ratios of fossil WIOC to fossil EC to typical primary OC-to-EC ratios from fossil sources including both coal combustion and vehicle emissions. The results suggest that fossil WIOC and fossil WSOC are probably a better approximation for primary and secondary fossil OC, respectively, than POCfossil and SOCfossil estimated using the EC tracer method.

[en] The structures of two manganese(II) complexes of 1,3,5-triaza-7-phosphaadamantane (PTA) reveal the first transition-metal complexes of PTA in which the metal preferentially coordinates to a nitrogen and not the phosphorus of PTA. The coordination environment about the manganese was probed using X-ray crystallography (solid state) and EXAFS spectroscopy (solution)

[en] This report presents information and data in support of a cost-benefit analysis being performed by Fair child Industries (FI) on the feasibility of retrieving existing US space nuclear systems in earth orbit by the Space Shuttle. This report evaluates, for US space nuclear systems presently in orbit, the radioisotopic inventory and external radiation field as a function of time, the effect of aging on fuel containment materials over the projected lifetime of the system, and the possible radioactive source terms should reentry eventually occur. Although the radioisotopic inventories and radiation fields have been evaluated for all systems, Transit 4A and Transit Triad have been emphasized in the evaluation of the aging effects and reentry consequences because these spacecraft have the shortest projected orbital lifetimes (570 and 150 years, respectively). In addition to existing systems in orbit, the radioisotopic inventory, radiation field, and reentry source terms have been evaluated for a General Purpose Heat Source (GPHS) in a parking orbit due to an aborted Galileo Mission or International Solar Polar Mission (ISPM)

[en] A new method of numerical calculation, based on geometrical optics for X-rays rather than ray-tracing, is developed to simulate the focal spot size and intensity gain from an elliptically-tapered one-bounce glass mono-capillary. Numerical results for a capillary designed for protein crystallography are in good agreement with experimental measurements and confirm a capillary slope errors limitation on the image quality

[en] A single, borosilicate-glass capillary was drawn into a 30.5 cm long elliptical shape. The inside diameter was 0.40 mm at the large base end and 0.13 mm at the tip. With 12 keV X-rays from the CHESS D1 bending magnet, the single-bounce capillary produced a focus of better than 18 μm in diameter (FHWM) at a 3 cm distance from the capillary tip. A flux gain of 110 in the focus position was observed along with a total flux in the spot of 4x10¹⁰ X-rays/s (conditions: 5.3 GeV, 182 mA, 1.5% bandwidth multilayer, 12 keV X-rays). A measurement of the far field focus ring diameter yielded a divergence of 3.8 mrad, in good agreement with the 4 mrad design of the optic for protein crystallography. Using a small 25 μm square beam, we measured the local reflectivity to be greater than 95% and the inner slope errors of the capillary to average about ±150 μrad, both from raw and elliptically shaped tubing. Our conclusion is that more perfect starting tubing (i.e. one with lower slope errors) is needed to make even more perfect elliptically figured optics in the future

No abstract available

[en] One of the challenges of tuning bimorph mirrors with many electrodes is that the calculated focusing voltages can be different by more than the safety limit (such as 500 V for the mirrors used at 17-ID at the Advanced Photon Source) between adjacent electrodes. A study of this problem at 17-ID revealed that the inverse problem of the tuning in situ, using X-rays, became ill-conditioned when the number of electrodes was large and the calculated focusing voltages were contaminated with measurement errors. Increasing the number of beamlets during the tuning could reduce the matrix condition number in the problem, but obtaining voltages with variation below the safety limit was still not always guaranteed and multiple iterations of tuning were often required. Applying Tikhonov regularization and using the L-curve criterion for the determination of the regularization parameter made it straightforward to obtain focusing voltages with well behaved variations. Some characteristics of the tuning results obtained using Tikhonov regularization are given in this paper.