Journal articles: 'Exit wave function'

1

Chevalier, J. P., and M. J. Hytch. "Simulating the exit wave function for uniformly disordered systems." Ultramicroscopy 52, no. 3-4 (December 1993): 253–59. http://dx.doi.org/10.1016/0304-3991(93)90033-t.

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Van Dyck, D., and J. H. Chen. "Towards an exit wave in closed analytical form." Acta Crystallographica Section A Foundations of Crystallography 55, no. 2 (March 1, 1999): 212–15. http://dx.doi.org/10.1107/s0108767398011337.

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A simple but sufficiently accurate expression is obtained for the exit wave of a crystal in zone-axis orientation. The exit wave at each atom column can be parametrized with only one parameter, which is a function of the projected `weight' of the column.

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Volkov, V., J. Wall, and Y. Zhu. "Exit Wave Function Retrieval from Diffraction Patterns with Variable SAED Aperture." Microscopy and Microanalysis 12, S02 (July 31, 2006): 1670–71. http://dx.doi.org/10.1017/s1431927606067122.

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Hohenstein, M. "Reconstruction of the exit surface wave function from experimental HRTEM micrographs." Ultramicroscopy 35, no. 2 (February 1991): 119–29. http://dx.doi.org/10.1016/0304-3991(91)90096-o.

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Bierwolf, R., and M. Hohenstein. "Premise-free reconstruction of the exit-surface wave function in HRTEM." Ultramicroscopy 56, no. 1-3 (November 1994): 32–45. http://dx.doi.org/10.1016/0304-3991(94)90144-9.

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Broeckx, J., M. Op de Beeck, and D. Van Dyck. "A useful approximation of the exit wave function in coherent STEM." Ultramicroscopy 60, no. 1 (August 1995): 71–80. http://dx.doi.org/10.1016/0304-3991(95)00053-4.

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Lee, Jongyeong, Yeongdong Lee, Jaemin Kim, and Zonghoon Lee. "Contrast Transfer Function-Based Exit-Wave Reconstruction and Denoising of Atomic-Resolution Transmission Electron Microscopy Images of Graphene and Cu Single Atom Substitutions by Deep Learning Framework." Nanomaterials 10, no. 10 (October 6, 2020): 1977. http://dx.doi.org/10.3390/nano10101977.

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The exit wave is the state of a uniform plane incident electron wave exiting immediately after passing through a specimen and before the atomic-resolution transmission electron microscopy (ARTEM) image is modified by the aberration of the optical system and the incoherence effect of the electron. Although exit-wave reconstruction has been developed to prevent the misinterpretation of ARTEM images, there have been limitations in the use of conventional exit-wave reconstruction in ARTEM studies of the structure and dynamics of two-dimensional materials. In this study, we propose a framework that consists of the convolutional dual-decoder autoencoder to reconstruct the exit wave and denoise ARTEM images. We calculated the contrast transfer function (CTF) for real ARTEM and assigned the output of each decoder to the CTF as the amplitude and phase of the exit wave. We present exit-wave reconstruction experiments with ARTEM images of monolayer graphene and compare the findings with those of a simulated exit wave. Cu single atom substitution in monolayer graphene was, for the first time, directly identified through exit-wave reconstruction experiments. Our exit-wave reconstruction experiments show that the performance of the denoising task is improved when compared to the Wiener filter in terms of the signal-to-noise ratio, peak signal-to-noise ratio, and structural similarity index map metrics.

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de Ruijter, W. J., M. R. McCartney, David J. Smith, and J. K. Weiss. "Exit-surface wave reconstruction using a focal series." Proceedings, annual meeting, Electron Microscopy Society of America 50, no. 2 (August 1992): 988–89. http://dx.doi.org/10.1017/s0424820100129577.

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Further advances in resolution enhancement of transmission electron microscopes can be expected from digital processing of image data recorded with slow-scan CCD cameras. Image recording with these new cameras is essential because of their high sensitivity, extreme linearity and negligible geometric distortion. Furthermore, digital image acquisition allows for on-line processing which yields virtually immediate reconstruction results. At present, the most promising techniques for exit-surface wave reconstruction are electron holography and the recently proposed focal variation method. The latter method is based on image processing applied to a series of images recorded at equally spaced defocus.Exit-surface wave reconstruction using the focal variation method as proposed by Van Dyck and Op de Beeck proceeds in two stages. First, the complex image wave is retrieved by data extraction from a parabola situated in three-dimensional Fourier space. Then the objective lens spherical aberration, astigmatism and defocus are corrected by simply dividing the image wave by the wave aberration function calculated with the appropriate objective lens aberration coefficients which yields the exit-surface wave.

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Haigh, S. J., H. Sawada, and Angus I. Kirkland. "Optimal tilt magnitude determination for aberration-corrected super resolution exit wave function reconstruction." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 367, no. 1903 (September 28, 2009): 3755–71. http://dx.doi.org/10.1098/rsta.2009.0124.

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Transmission electron microscope (TEM) images recorded under tilted illumination conditions transfer higher spatial frequencies than axial images. This super resolution information transfer is highly directional in a single image, but can be extended in all directions through the use of complementary beam tilts during exit wave function reconstruction. We have determined the optimal experimental tilt magnitude for aperture synthesis in an aberration-corrected TEM. It is shown that electron-optical aberration correction allows the use of larger tilt angles and reduces the constraints that are imposed on experimental data acquisition in an uncorrected microscope. We demonstrate that, in many cases, the resolution improvement achievable is now limited by the sample and not by instrumental parameters. An exit wave function is presented that has been successfully reconstructed from a dataset of aberration-corrected images, including images acquired at a beam tilt of 18 mrad, which clearly demonstrates a resolution improvement from 0.11 nm to better than 0.08 nm at 200 kV.

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Sayagués, Maria, Katherine Titmuss, Rudiger Meyer, Angus Kirkland, Jeremy Sloan, John Hutchison, and Richard Tilley. "Structural characterization of the n = 5 layered perovskite neodymium titanate using high-resolution transmission electron microscopy and image reconstruction." Acta Crystallographica Section B Structural Science 59, no. 4 (July 25, 2003): 449–55. http://dx.doi.org/10.1107/s0108768103010346.

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The structure of Nd5Ti5O17 has been refined from a reconstruction of the specimen exit-plane wave restored from a series of incrementally defocused high-resolution transmission electron microscope (HRTEM) images. The phase of the exit-plane wave shows contrast attributable to the oxygen anion sublattice and coupled with simulations provides confirmation of the composition of the cation sites as a function of sample thickness. The enhanced resolution in the exit-plane wave additionally allows a direct measurement of the `skewing' of the perovskite slabs.

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Kirkland, Angus I., Rüdiger R. Meyer, and Lan-Yun Shery Chang. "Local Measurement and Computational Refinement of Aberrations for HRTEM." Microscopy and Microanalysis 12, no. 6 (October 11, 2006): 461–68. http://dx.doi.org/10.1017/s1431927606060612.

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Methods for accurate and automated determination of the coefficients of the wave aberration function are compared with particular emphasis on measurements of higher order coefficients in corrected instruments. Experimental applications of aberration measurement to the determination of illumination isoplanicity and high precision local refinement of restored exit waves are also described.

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12

Gribelyuk, M. A., and J. L. Hutchison. "On the iterative restoration of exit plane wave function from defocus series in HREM." Proceedings, annual meeting, Electron Microscopy Society of America 49 (August 1991): 550–51. http://dx.doi.org/10.1017/s0424820100087069.

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The validity domain of a Multiple Image MAximum Posteriori (MIMAP) approach has been estimated on UMo5O16 complex oxide structure (Fig.1). Model defocus series (both noise-free and with an additive random noise) have been prepared by multislice method with no objective aperture imposed. Defocus values Δfn=((8n+3)Csλ/2)05 (n=0,...,4) corresponded to plateaus of JEOL-4000EX microscope transfer function operated under U=400kV. The following problems are considered:Self-consistency. Apart from a wave function MIMAP aims at refinement of translational misalignment, difference in defocus values within series and a “fog” level c0. The latter represents an additive constant to image intensity arising by image recording and manipulation. We assumed that defocus values were known exactly and images were perfectly aligned. If one sets c01 to its exact value c0=0 and starts restoration from noise-free defocus series of a t=12 thin crystal the procedure will diverge (Fig.2).

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Umemura, Akira. "Self-destabilising loop of a low-speed water jet emanating from an orifice in microgravity." Journal of Fluid Mechanics 797 (May 16, 2016): 146–80. http://dx.doi.org/10.1017/jfm.2016.271.

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A one-dimensional global mode analysis is conducted for low-speed water jets emanating from a circular orifice in microgravity, in which the observed spontaneous convective instability causes almost periodic jet disintegrations at a fixed location for each jet-issue speed that exceeds a certain threshold. The inviscid spatial linear stability analysis identifies four wave modes excitable at the frequency: the Plateau–Rayleigh (PR) unstable wave, its complex conjugate and two neutral waves which may transfer energy upstream. Their linear combination satisfying the orifice exit condition may describe the synchronised reproduction of a PR unstable wave from each neutral wave at the orifice exit. On the other hand, a weakly nonlinear analysis shows that the growth of the nonlinear PR unstable wave produces the two neutral waves near the orifice. Thus, the same PR unstable wave can be reproduced on a newly issued liquid surface owing to the neutral waves produced by its own nonlinear growth. This self-destabilising loop, dominantly operating for the most unstable PR wave, determines the initial PR unstable wave amplitude and, consequently, the breakup length as a function of jet-issue speed. The predicted initial amplitude of the PR unstable wave is in reasonably good agreement with the value calculated from the average breakup length measured in our microgravity experiments. It is found that that the loop consists mainly of the downstream- and upstream-moving neutral waves at relatively high and low jet speeds, respectively. The stability of the self-destabilising loop is also discussed.

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Lukas, André, and Rudolf Poppe. "Decoherence in Pre-Big-Bang Cosmology." Modern Physics Letters A 12, no. 09 (March 21, 1997): 597–612. http://dx.doi.org/10.1142/s0217732397000625.

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We analyze the quantum cosmology of the simplest pre-big-bang model without dilaton potential. In addition to the minisuperspace variables we include inhomogeneous dilaton fluctuations and determine their wave function on a semiclassical background. This wave function is used to calculate the reduced density matrix and to find criteria for the loss of decoherence. It is shown that coherence between different backgrounds can always be achieved by a specific choice of vacua. Their exact expressions as functions of the wave number and the background quantities are given. Generically, however, decoherence can be expected. In particular, we discuss the implications of these results on the "exit problem" of pre-big-bang cosmology.

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15

Gribelyuk, M. A., and J. L. Hutchison. "On the iterative restoration of the exit plane wave function from defocus series in HREM." Ultramicroscopy 45, no. 1 (August 1992): 127–43. http://dx.doi.org/10.1016/0304-3991(92)90044-k.

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Kirkland, Angus I., and Rüdiger R. Meyer. "“Indirect” High-Resolution Transmission Electron Microscopy: Aberration Measurement and Wavefunction Reconstruction." Microscopy and Microanalysis 10, no. 4 (August 2004): 401–13. http://dx.doi.org/10.1017/s1431927604040437.

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Improvements in instrumentation and image processing techniques mean that methods involving reconstruction of focal or beam-tilt series of images are now realizing the promise they have long offered. This indirect approach recovers both the phase and the modulus of the specimen exit plane wave function and can extend the interpretable resolution. However, such reconstructions require thea posterioridetermination of the objective lens aberrations, including the actual beam tilt, defocus, and twofold and threefold astigmatism. In this review, we outline the theory behind exit plane wavefunction reconstruction and describe methods for the accurate and automated determination of the required coefficients of the wave aberration function. Finally, recent applications of indirect reconstruction in the structural analysis of complex oxides are presented.

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17

Sivasegaram, S., and J. H. Whitelaw. "Combustion Oscillations in Dump Combustors with a Constricted Exit." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 202, no. 3 (May 1988): 205–10. http://dx.doi.org/10.1243/pime_proc_1988_202_108_02.

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Combustion oscillations in axisymmetric dump combustors have been examined in terms of amplitude and frequency characteristics for two dump-plane area ratios and as a function of combustor length, exit constriction, diameter, flowrate, equivalence ratio and swirl. The flammability limits are similar to those previously determined in disc- and dump-stabilized flames without a constricted exit, but the stability limits are not. Rough combustion, characterized by radiated sound levels more than 12 dB above that in smooth combustion, was observed at equivalence ratios close to the flammability limits for values of swirl number less than 0.2 and was associated with the bulk-mode frequency. With swirl numbers in the range from 0.2 to 0.4, rough combustion was not encountered and, for higher values, existed in a range of equivalence ratios from around 0.8 to 1.4, provided the combustor length and flowrate led to half-wave frequencies less than around 800 Hz. In those ranges of equivalance ratio where the combustion was smooth, discrete frequencies corresponding to the bk-mode and half-wave were observed. The amplitude of the discrete frequency increased when it coincided with the shedding frequency of the shear layer.

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Lin, Fang, and Chuanhong Jin. "Inverse problem of the multislice method in retrieving projected complex potentials from the exit-wave function." Micron 58 (March 2014): 47–54. http://dx.doi.org/10.1016/j.micron.2013.11.005.

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19

Thust, A., M. Lentzen, and K. Urban. "Non-linear reconstruction of the exit plane wave function from periodic high-resolution electron microscopy images." Ultramicroscopy 53, no. 2 (February 1994): 101–20. http://dx.doi.org/10.1016/0304-3991(94)90002-7.

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SANYAL, ABHIK KUMAR, and BIJAN MODAK. "EXTENDED INFLATION— A QUANTUM-COSMOLOGICAL SURVEY." International Journal of Modern Physics A 07, no. 17 (July 10, 1992): 4039–52. http://dx.doi.org/10.1142/s0217751x92001800.

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This paper considers the Einstein-Brans-Dicke action coupled with a Higgs sector. It is shown that a graceful exit from inflation is not possible, rejecting the claim of La and Steinhardt. Further, wormhole solutions with and without conserved charges are explored. Finally, the wave function of the universe in this model is constructed with the boundary condition, as proposed by Vilenkin. The interesting feature of the wave function is that it has been constructed for an arbitrary factor-ordering index.

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Kawasaki, T., M. Taya, T. Nomaguchi, and Y. Takai. "Effective phase correction function for high-resolution exit wave reconstruction by a three-dimensional Fourier filtering method." Ultramicroscopy 102, no. 2 (January 2005): 127–39. http://dx.doi.org/10.1016/j.ultramic.2004.09.004.

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22

Bhattacharyya, Somnath, Christoph T. Koch, and Manfred Rühle. "Projected potential profiles across interfaces obtained by reconstructing the exit face wave function from through focal series." Ultramicroscopy 106, no. 6 (April 2006): 525–38. http://dx.doi.org/10.1016/j.ultramic.2006.01.007.

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23

Lentzen, M., and K. Urban. "Reconstruction of the projected crystal potential from a periodic high-resolution electron microscopy exit plane wave function." Ultramicroscopy 62, no. 1-2 (January 1996): 89–102. http://dx.doi.org/10.1016/0304-3991(95)00091-7.

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Thust, A., and C. L. Jia. "Atomic Structure Determination Using the Focal-Series Reconstruction Technique." Microscopy and Microanalysis 7, S2 (August 2001): 286–87. http://dx.doi.org/10.1017/s1431927600027501.

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During the last five years the technique focal-series reconstruction has evolved to a powerful tool for investigating materials science problems in high-resolution transmission electron microscopy. Compared to the conventional interpretation of one single high-resolution image, the quantum mechanical electron wave function at the exit plane of the object (exit-plane wave function, EPW) is in many cases a better starting point for the materials analysis. The retrieval of the EPW is achieved on a routine basis by applying automated numerical procedures to a series of images taken from the same specimen area at different objective lens defocus values. The application of the reconstruction procedure allows one to remove numerically all the well known instrumental artifacts, such as nonlinear contrast formation or delocalisation effects due to spherical aberration and other parasitic aberrations. The reconstructed EPW gives thus direct insight into the atomic structure in the case of sufficiently thin objects and renders tedious image simulations of complicated defects unnecessary in many cases.

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Condori, R. Pampa, H. Dias, and J. Lubian. "Using a double folding potential for the derivation of the spectroscopic factors of the (3He, d) transfer reaction." International Journal of Modern Physics E 25, no. 09 (September 2016): 1650061. http://dx.doi.org/10.1142/s0218301316500610.

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In this paper, the [Formula: see text] reactions are revisited, with the goal of obtaining spectroscopic factors (SF) for the transition to the ground state of some residual nuclei, applying the distorted wave Born approximation (DWBA). The double-folding São Paulo Potential (SPP) was used to derive the distorted wave function in the entrance and exit channels. The derived SF are compared with the results of extensive shell model calculations showing a rather good agreement.

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Andreianov, Boris, Carlotta Donadello, and Massimiliano D. Rosini. "Crowd dynamics and conservation laws with nonlocal constraints and capacity drop." Mathematical Models and Methods in Applied Sciences 24, no. 13 (September 17, 2014): 2685–722. http://dx.doi.org/10.1142/s0218202514500341.

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In this paper we model pedestrian flows evacuating a narrow corridor through an exit by a one-dimensional hyperbolic conservation law with a point constraint in the spirit of [Colombo and Goatin, J. Differential Equations, 2007]. We introduce a nonlocal constraint to restrict the flux at the exit to a maximum value p(ξ), where ξ is the weighted averaged instantaneous density of the crowd in an upstream vicinity of the exit. Choosing a non-increasing constraint function p(⋅), we are able to model the capacity drop phenomenon at the exit. Existence and stability results for the Cauchy problem with Lipschitz constraint function p(⋅) are achieved by a procedure that combines the wave-front tracking algorithm with the operator splitting method. In view of the construction of explicit examples (one is provided), we discuss the Riemann problem with discretized piecewise constant constraint p(⋅). We illustrate the fact that nonlocality induces loss of self-similarity for the Riemann solver; moreover, discretization of p(⋅) may induce non-uniqueness and instability of solutions.

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27

Rez, Peter. "Analytic integration of contrast transfer functions." Proceedings, annual meeting, Electron Microscopy Society of America 46 (1988): 822–23. http://dx.doi.org/10.1017/s042482010010617x.

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In high resolution microscopy the image amplitude is given by the convolution of the specimen exit surface wave function and the microscope objective lens transfer function. This is usually done by multiplying the wave function and the transfer function in reciprocal space and integrating over the effective aperture. For very thin specimens the scattering can be represented by a weak phase object and the amplitude observed in the image plane is1where fe (Θ) is the electron scattering factor, r is a postition variable, Θ a scattering angle and x(Θ) the lens transfer function. x(Θ) is given by2where Cs is the objective lens spherical aberration coefficient, the wavelength, and f the defocus.We shall consider one dimensional scattering that might arise from a cross sectional specimen containing disordered planes of a heavy element stacked in a regular sequence among planes of lighter elements. In a direction parallel to the disordered planes there will be a continuous distribution of scattering angle.

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Lin, F., Qing Chen, and Lian Mao Peng. "A New Scheme for the Exit-Wave Reconstruction from a Small Set of Focus Series of HREM Images." Materials Science Forum 475-479 (January 2005): 4059–62. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.4059.

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A new procedure is proposed for the exit electron wave reconstruction using a small set of high-resolution electron microscopy (HREM) images. This procedure is similar to that proposed by van Dyck and coworkers, but the relative shifts between different HREM images are obtained via the genetic algorithm instead of the more widely used cross-correlation function (XCF) method. The new procedure is demonstrated using simulated HREM images with added noise, and shown to be able to deal with situation where the scheme based on the method of XCF is not applicable.

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Нечай, А. Н., А. А. Перекалов, Н. И. Чхало, and Н. Н. Салащенко. "Наблюдение лазерной искры на скачке уплотнения в газоструйной мишени." Письма в журнал технической физики 45, no. 19 (2019): 14. http://dx.doi.org/10.21883/pjtf.2019.19.48310.17862.

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The problem of degradation of gas nozzles is relevant in designing of high-power laser-plasma sources of extreme ultraviolet radiation with a gas jet as a target. Degradation is observed due to insufficient removal of the zone of formation of a laser spark from the nozzle exit. A cardinal solution of this problem is proposed due to the formation of a laser spark on shock waves, which are specially formed during the outflow of a supersonic gas jet. In this work, a laser spark was obtained on a similar shock wave and the emission intensity was measured as a function of the geometrical location of the spark formation.

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Gaberšek, Saša, and Dale R. Durran. "Gap Flows through Idealized Topography. Part I: Forcing by Large-Scale Winds in the Nonrotating Limit." Journal of the Atmospheric Sciences 61, no. 23 (December 1, 2004): 2846–62. http://dx.doi.org/10.1175/jas-3340.1.

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Abstract Gap winds produced by a uniform airstream flowing over an isolated flat-top ridge cut by a straight narrow gap are investigated by numerical simulation. On the scale of the entire barrier, the proportion of the oncoming flow that passes through the gap is relatively independent of the nondimensional mountain height ε, even over that range of ε for which there is the previously documented transition from a “flow over the ridge” regime to a “flow around” regime. The kinematics and dynamics of the gap flow itself were investigated by examining mass and momentum budgets for control volumes at the entrance, central, and exit regions of the gap. These analyses suggest three basic behaviors: the linear regime (small ε) in which there is essentially no enhancement of the gap flow; the mountain wave regime (ε ∼ 1.5) in which vertical mass and momentum fluxes play a crucial role in creating very strong winds near the exit of the gap; and the upstream-blocking regime (ε ∼ 5) in which lateral convergence generates the strongest winds near the entrance of the gap. Trajectory analysis of the flow in the strongest events, the mountain wave events, confirms the importance of net subsidence in creating high wind speeds. Neglect of vertical motion in applications of Bernoulli's equation to gap flows is shown to lead to unreasonable wind speed predictions whenever the temperature at the gap exit exceeds that at the gap entrance. The distribution of the Bernoulli function on an isentropic surface shows a correspondence between regions of high Bernoulli function and high wind speeds in the gap-exit jet similar to that previously documented for shallow-water flow.

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Wang, Y. Y., M. Gribelyuk, A. Domenicucci, J. Bruley, J. Gaudiello, and M. Kawasaki. "Variable Magnification Electron Holography for 2-D Mapping of Semiconductor Devices." Microscopy Today 12, no. 6 (November 2004): 20–25. http://dx.doi.org/10.1017/s1551929500065925.

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The exit electron wave from transmission electron microscopy (TEM) specimens contains both amplitude and phase information. In routine TEM imaging, only amplitude information is recorded on the recording devices (film or CCD camera) and phase information of the electron wave function normally is canceled out.In 1947, Dennis Gabor proposed off-axis electron holography, a method of interference imaging in which the phase and amplitude components of the electron beam are obtained to correct spherical aberration of the transmission electron microscope to improve spatial resolution. In that process, the electron beam is split into the two beams: the un-scattered electron beam (i.e. the reference wave) and the image beam (or object wave) diffracted by the specimen and exiting the bottom of the specimen surface.

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MAHALINGAM, K., K. G. EYINK, G. J. BROWN, and D. L. DORSEY. "APPLICATION OF EXIT-PLANE WAVE FUNCTION IMAGES IN HIGH-RESOLUTION TRANSMISSION ELECTRON MICROSCOPY FOR QUANTITATIVE ANALYSIS OF III–V SEMICONDUCTOR INTERFACES." International Journal of Nanoscience 03, no. 06 (December 2004): 723–28. http://dx.doi.org/10.1142/s0219581x04002668.

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An image simulation study is performed to investigate the applicability of exit-plane wave function (EPWF) images for an atomic-level compositional mapping of interfaces in the GaAs – AlAs system. A simple procedure for quantifying the composition across an interface, which is based on the method of factorial analysis of correspondence is proposed. A test of this procedure on a simulated EPWF-phase image of Al 0.4 Ga 0.6 As/GaAs/Al 0.4 Ga 0.6 As structure, with an atomically abrupt interface on one side and a graded interface on the other, yields profiles which mimic the model-profiles.

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Kweon, Y. H., H. D. Kim, T. Aoki, and T. Setoguchi. "A study of the impulse waves discharged from convergent and divergent ducts." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 218, no. 12 (December 1, 2004): 1469–79. http://dx.doi.org/10.1243/0954406042690443.

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The present study describes experimental and computational works to investigate impulse waves that are generated by discharge of a compression pulse from the exit of convergent and divergent ducts. The objective of the present study is to compare the impulse waves discharged from a straight duct with those discharged from convergent and divergent ducts. Computational analysis is performed using the axisymmetric, unsteady, inviscid, compressible, Euler equations. A second-order total variation diminishing finite difference scheme is used to solve the governing equation system. Experiment is carried out in a simple shock tube with an open end. Convergent and divergent ducts are connected to the open end of the shock tube. Initial compression pulses with different overpressures and wavelengths are made at the entrance of the convergent and divergent ducts. The present computational method predicts the measured impulse waves well. The results obtained show that for a given duct the magnitude of the impulse wave decreases as the wavelength of the initial compression pulse increases and it is a weakly increasing function of the overpressure of the initial compression pulse. Compared with a straight duct, a convergent duct leads to a weaker impulse wave, while a divergent duct causes a stronger impulse wave. It is therefore believed that the convergent duct can be a passive control device used to reduce the magnitude of the impulse wave.

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Bošnjak, Roman, and Mitja Benedièiè. "Direct epidural electrical stimulation of the optic nerve: a new method for intraoperative assessment of function." Journal of Neurosurgery 109, no. 4 (October 2008): 647–53. http://dx.doi.org/10.3171/jns/2008/109/10/0647.

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Intraoperative visual system monitoring of lesions with a close relationship to the optic apparatus by using light flashes reportedly is difficult to perform, and the results are too unreliable to interpret. The authors used direct epidural electrical stimulation of the optic nerve (ON) during surgery instead of light flashes. Four patients were included in this feasibility study. In 3 patients—1 each harboring a planum sphenoidale meningioma, a tuberculum sellae meningioma, and an intraorbital ON sheath meningioma—2 stimulating needle electrodes were placed on each side of the ON just anterior to the optic canal, before unroofing the optic canal and an extradural anterior clinoidectomy. In the fourth patient, who harbored a frontotemporal astrocytoma, stimulation was applied at the exit of the ON from the canal. The electrically induced visual evoked potentials (eVEPs) were recorded from the scalp before, during, and after tumor removal. A typical eVEP consisted of N20 and N40 waves. The amplitude of the N40 wave varied up to 25% prior to tumor removal. In the patient with a symptomatic tuberculum sellae meningioma, the decompressive effect of opening the optic canal and the impact of manipulation during piecemeal tumor removal were detected by the eVEPs. In the patient with an ON sheath meningioma and light sensation, only the N20 wave was observed. Epidural electrical stimulation of the ON is a safe means of providing a stable signal and real-time information on nerve conduction during surgery. It may be a useful adjunct in improving visual outcomes postoperatively. Further clinical studies are necessary.

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Jesson, D. E., and S. J. Pennycook. "Atomic Imaging of Crystals using Large-Angle Electron Scattering in STEM." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 1 (August 12, 1990): 74–75. http://dx.doi.org/10.1017/s0424820100179129.

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It is well known that conventional atomic resolution electron microscopy is a coherent imaging process best interpreted in reciprocal space using contrast transfer function theory. This is because the equivalent real space interpretation involving a convolution between the exit face wave function and the instrumental response is difficult to visualize. Furthermore, the crystal wave function is not simply related to the projected crystal potential, except under a very restrictive set of experimental conditions, making image simulation an essential part of image interpretation. In this paper we present a different conceptual approach to the atomic imaging of crystals based on incoherent imaging theory. Using a real-space analysis of electron scattering to a high-angle annular detector, it is shown how the STEM imaging process can be partitioned into components parallel and perpendicular to the relevant low index zone-axis.It has become customary to describe STEM imaging using the analytical treatment developed by Cowley. However, the convenient assumption of a phase object (which neglects the curvature of the Ewald sphere) fails rapidly for large scattering angles, even in very thin crystals. Thus, to avoid unpredictive numerical solutions, it would seem more appropriate to apply pseudo-kinematic theory to the treatment of the weak high angle signal. Diffraction to medium order zero-layer reflections is most important compared with thermal diffuse scattering in very thin crystals (<5nm). The electron wave function ψ(R,z) at a depth z and transverse coordinate R due to a phase aberrated surface probe function P(R-RO) located at RO is then well described by the channeling approximation;

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Vázquez-Báez, V., and C. Ramírez. "Quantum Cosmology of Quadratic f(R) Theories with a FRW Metric." Advances in Mathematical Physics 2017 (2017): 1–5. http://dx.doi.org/10.1155/2017/1056514.

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We study the quantum cosmology of a quadratic fR theory with a FRW metric, via one of its equivalent Horndeski type actions, where the dynamic of the scalar field is induced. The classical equations of motion and the Wheeler-DeWitt equation, in their exact versions, are solved numerically. There is a free parameter in the action from which two cases follow: inflation + exit and inflation alone. The numerical solution of the Wheeler-DeWitt equation depends strongly on the boundary conditions, which can be chosen so that the resulting wave function of the universe is normalizable and consistent with Hermitian operators.

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Tillmann, K., A. Thust, and K. Urban. "Spherical Aberration Correction in Tandem with Exit-Plane Wave Function Reconstruction: Interlocking Tools for the Atomic Scale Imaging of Lattice Defects in GaAs." Microscopy and Microanalysis 10, no. 02 (March 17, 2004): 185–98. http://dx.doi.org/10.1017/s1431927604040395.

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Kahane, Nitza, Yuval Cinnamon, Ido Bachelet, and Chaya Kalcheim. "The third wave of myotome colonization by mitotically competent progenitors: regulating the balance between differentiation and proliferation during muscle development." Development 128, no. 12 (June 15, 2001): 2187–98. http://dx.doi.org/10.1242/dev.128.12.2187.

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The myotome is formed by a first wave of pioneer cells originating from the entire dorsomedial region of epithelial somites and a second wave that derives from all four lips of the dermomyotome but generates myofibers from only the rostral and caudal edges. Because the precedent progenitors exit the cell cycle upon myotome colonization, subsequent waves must account for consecutive growth. In this study, double labeling with CM-DiI and BrdU revealed the appearance of a third wave of progenitors that enter the myotome as mitotically active cells from both rostral and caudal dermomyotome edges. These cells express the fibroblast growth factor (FGF) receptor FREK and treatment with FGF4 promotes their proliferation and redistribution towards the center of the myotome. Yet, they are negative for MyoD, Myf5 and FGF4, which are, however, expressed in myofibers.The proliferating progenitors first appear around the 30-somite stage in cervical-level myotomes and their number continuously increases, making up 85% of total muscle nuclei by embryonic day (E)4. By this stage, generation of second-wave myofibers, which also enter from the extreme lips is still under way. Formation of the latter fibers peaks at 30 somites and progressively decreases with age until E4. Thus, cells in these dermomyotome lips generate simultaneously distinct types of muscle progenitors in changing proportions as a function of age. Consistent with a heterogeneity in the cellular composition of the extreme lips, MyoD is normally expressed in only a subset of these epithelial cells. Treatment with Sonic hedgehog drives most of them to become MyoD positive and then to become myofibers, with a concurrent reduction in the proportion of proliferating muscle precursors.

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Yan, Ada W. C., Adrian J. D’Alfonso, Andrew J. Morgan, Corey T. Putkunz, and Leslie J. Allen. "Fast Deterministic Ptychographic Imaging Using X-Rays." Microscopy and Microanalysis 20, no. 4 (May 23, 2014): 1090–99. http://dx.doi.org/10.1017/s1431927614000932.

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AbstractWe present a deterministic approach to the ptychographic retrieval of the wave at the exit surface of a specimen of condensed matter illuminated by X-rays. The method is based on the solution of an overdetermined set of linear equations, and is robust to measurement noise. The set of linear equations is efficiently solved using the conjugate gradient least-squares method implemented using fast Fourier transforms. The method is demonstrated using a data set obtained from a gold–chromium nanostructured test object. It is shown that the transmission function retrieved by this linear method is quantitatively comparable with established methods of ptychography, with a large decrease in computational time, and is thus a good candidate for real-time reconstruction.

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Piovesan, Tommaso, Andrea Magrini, and Ernesto Benini. "Accurate 2-D Modelling of Transonic Compressor Cascade Aerodynamics." Aerospace 6, no. 5 (May 19, 2019): 57. http://dx.doi.org/10.3390/aerospace6050057.

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Modern aeronautic fans are characterised by a transonic flow regime near the blade tip. Transonic cascades enable higher pressure ratios by a complex system of shockwaves arising across the blade passage, which has to be correctly reproduced in order to predict the performance and the operative range. In this paper, we present an accurate two-dimensional numerical modelling of the ARL-SL19 transonic compressor cascade. A large series of data from experimental tests in supersonic wind tunnel facilities has been used to validate a computational fluid dynamic model, in which the choice of turbulence closure resulted critical for an accurate reproduction of shockwave-boundary layer interaction. The model has been subsequently employed to carry out a parametric study in order to assess the influence of main flow variables (inlet Mach number, static pressure ratio) and geometric parameters (solidity) on the shockwave pattern and exit status. The main objectives of the present work are to perform a parametric study for investigating the effects of the abovementioned variables on the cascade performance, in terms of total-pressure loss coefficient, and on the shockwave pattern and to provide a quite large series of data useful for a preliminary design of a transonic compressor rotor section. After deriving the relation between inlet and exit quantities, peculiar to transonic compressors, exit Mach number, mean exit flow angle and total-pressure loss coefficient have been examined for a variety of boundary conditions and parametrically linked to inlet variables. Flow visualisation has been used to describe the shock-wave pattern as a function of the static pressure ratio. Finally, the influence of cascade solidity has been examined, showing a potential reduction of total-pressure loss coefficient by employing a higher solidity, due to a significant modification of shockwave system across the cascade.

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Wessels, Deborah, Rebecca Brincks, Spencer Kuhl, Vesna Stepanovic, Karla J. Daniels, Gerald Weeks, Chinten J. Lim, et al. "RasC Plays a Role in Transduction of Temporal Gradient Information in the Cyclic-AMP Wave of Dictyostelium discoideum." Eukaryotic Cell 3, no. 3 (June 2004): 646–62. http://dx.doi.org/10.1128/ec.3.3.646-662.2004.

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ABSTRACT To define the role that RasC plays in motility and chemotaxis, the behavior of a rasC null mutant, rasC −, in buffer and in response to the individual spatial, temporal, and concentration components of a natural cyclic AMP (cAMP) wave was analyzed by using computer-assisted two-dimensional and three-dimensional motion analysis systems. These quantitative studies revealed that rasC − cells translocate at the same velocity and exhibit chemotaxis up spatial gradients of cAMP with the same efficiency as control cells. However, rasC − cells exhibit defects in maintaining anterior-posterior polarity along the substratum and a single anterior pseudopod when translocating in buffer in the absence of an attractant. rasC − cells also exhibit defects in their responses to both the increasing and decreasing temporal gradients of cAMP in the front and the back of a wave. These defects result in the inability of rasC − cells to exhibit chemotaxis in a natural wave of cAMP. The inability to respond normally to temporal gradients of cAMP results in defects in the organization of the cytoskeleton, most notably in the failure of both F actin and myosin II to exit the cortex in response to the decreasing temporal gradient of cAMP in the back of the wave. While the behavioral defect in the front of the wave is similar to that of the myoA −/myoF − myosin I double mutant, the behavioral and cytoskeletal defects in the back of the wave are similar to those of the S13A myosin II regulatory light-chain phosphorylation mutant. Expression array data support the premise that the behavioral defects exhibited by the rasC − mutant are the immediate result of the absence of RasC function.

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Kim, Hwang Su. "Atomic resolution improvement by a new method using the second derivative of the intensity function of the reconstructed exit wave of electrons for a thin β-Si3N4 crystal." Scripta Materialia 63, no. 5 (September 2010): 524–27. http://dx.doi.org/10.1016/j.scriptamat.2010.05.020.

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Zou, Xiaodong, and Sven Hovmöller. "Structure Determination at Atomic Resolution by Electron Crystallography." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 1 (August 12, 1990): 44–45. http://dx.doi.org/10.1017/s0424820100178975.

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Structure determination by electron microscopy is emerging as a serious competitor to the classical methods of X-ray diffraction. The main advantage of EM is that the phase information is restored in the image, whereas with X-ray diffraction it is lost.The structure determination of an inorganic crystal by electron microscopy would be trivial if the micrograph was just a magnified image of the electron density in the crystal. Unfortunately it is not. A limited number of non-linear effects distort the image. These effects can be divided into two parts; those arising already in the crystal and those that are due to optical distortions. For a crystal one unit cell thick the wave front at the exit surface of the crystal is a linear function of the electron density within the unit cell. As the crystals become thicker more and more of the diffracted electrons will have been doubly diffracted, making the image no longer a linear function of the electron density. For crystals thinner than half the mean free path for electrons most of the scattered electrons are still scattered only once, making the image interpretable.

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Pulido, Manuel, and John Thuburn. "The Seasonal Cycle of Gravity Wave Drag in the Middle Atmosphere." Journal of Climate 21, no. 18 (September 15, 2008): 4664–79. http://dx.doi.org/10.1175/2008jcli2006.1.

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Abstract Using a variational technique, middle atmosphere gravity wave drag (GWD) is estimated from Met Office middle atmosphere analyses for the year 2002. The technique employs an adjoint model of a middle atmosphere dynamical model to minimize a cost function that measures the differences between the model state and observations. The control variables are solely the horizontal components of GWD; therefore, the minimization determines the optimal estimate of the drag. For each month, Met Office analyses are taken as the initial condition for the first day of the month, and also as observations for each successive day. In this way a three-dimensional GWD field is obtained for the entire year with a temporal resolution of 1 day. GWD shows a pronounced seasonal cycle. During solstices, there are deceleration regions of the polar jet centered at about 63° latitude in the winter hemisphere, with a peak of 49 m s−1 day−1 at 0.24 hPa in the Southern Hemisphere; the summer hemisphere also shows a deceleration region but much weaker, with a peak of 24 m s−1 day−1 centered at 45° latitude and 0.6 hPa. During equinoxes GWD is weak and exhibits a smooth transition between the winter and summer situation. The height and latitude of the deceleration center in both winter and summer hemispheres appear to be constant. Important longitudinal dependencies in GWD are found that are related to planetary wave activity; GWD intensifies in the exit region of jet streaks. In the lower tropical stratosphere, the estimated GWD shows a westward GWD descending together with the westward phase of the quasi-biennial oscillation. Above, GWD exhibits a semiannual pattern that is approximately out of phase with the semiannual oscillation in the zonal wind. Furthermore, a descending GWD pattern is found at those heights, similar in magnitude and sign to that in the lower stratosphere.

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Coene, W. "A practical algorithm for maximum-likelihood HREM image reconstruction." Proceedings, annual meeting, Electron Microscopy Society of America 50, no. 2 (August 1992): 986–87. http://dx.doi.org/10.1017/s0424820100129565.

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Reconstruction in HREM of the complex wave function at the exit face of a crystal foil out of a focal series of HREM images, and with correction for the microscope's aberrations, can be performed with a variety of algorithms depending on the approximations involved for the HREM image formation. The maximum-a-posteriori (MAP) recursive reconstruction algorithm of Kirkland is the most general one with the full benefit of the effects of non-linear imaging and partial coherence, which are correctly treated in terms of a transmission-cross-coefficient (TCC). However, the routine application of the Kirkland algorithm has thusfar been hampered by its enormous computational demands, especially when large image frame sizes (5122) and a large number of HREM images (≥20) are aimed at. In this paper, we present a modified version of the Kirkland method within a maximum-likelihood (MAL) framework, and with a new numerical implementation yielding a workable algorithm with a much higher computational efficiency.

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Cherng, J. G., and Tsung-Yen Na. "Unsteady Isentropic Flow through Ducts with Prescribed Sound Pressure Level Distribution." Journal of Vibration and Acoustics 117, no. 3A (July 1, 1995): 279–84. http://dx.doi.org/10.1115/1.2874448.

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An analytical method for the determination of the required shape of a duct for a prescribed sound pressure level distribution is presented in this paper. The physical model involves a sound wave propagating in an unsteady flow of compressible fluids through ducts. Two cases are considered. In the first case, the channel shape, F(X), is given as either an exponential function or a linear function of the distance along the axis with an unknown parameter in the expression for F(X). The unknown parameter is determined by the prescribed ratio of the sound pressure level at the exit section of the duct to that at the entrance. In the second case, the sound pressure level is specified at every point along the length of the duct, and the duct shape, F(X), is sought. The governing differential equations of the model are presented. The method of complex superposition is used to separate the real and the imaginary parts of the perturbation quantities. The results show that the cross-sectional area is sensitive to the flow speed and the frequency of the sound source. Furthermore, a convergent/divergent duct has to be used to achieve a linear sound pressure level distribution.

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Van Dyck, D. "A Simple Real-Space Channelling Theory for Electron Diffraction and HREM." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 1 (August 12, 1990): 64–65. http://dx.doi.org/10.1017/s0424820100179075.

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The computation of the many beam dynamical electron diffraction amplitudes or high resolution images can only be done numerically by using rather sophisticated computer programs so that the physical insight in the diffraction progress is often lost. Furthermore, it is not likely that in this way the inverse problem can be solved exactly, i.e. to reconstruct the structure of the object from the knowledge of the wavefunction at its exit face, as is needed for a direct method [1]. For this purpose, analytical expressions for the electron wavefunction in real or reciprocal space are much more useful. However, the analytical expressions available at present are relatively poor approximations of the dynamical scattering which are only valid either for thin objects ((weak) phase object approximation, thick phase object approximation, kinematical theory) or when the number of beams is very limited (2 or 3). Both requirements are usually invalid for HREM of crystals. There is a need for an analytical expression of the dynamical electron wavefunction which applies for many beam diffraction in thicker crystals. It is well known that, when a crystal is viewed along a zone axis, i.e. parallel to the atom columns, the high resolution images often show a one-to-one correspondence with the configuration of columns provided the distance between the columns is large enough and the resolution of the instrument is sufficient. This is for instance the case in ordered alloys with a column structure [2,3]. From this, it can be suggested that, for a crystal viewed along a zone axis with sufficient separation between the columns, the wave function at the exit face does mainly depend on the projected structure, i.e. on the type of atom columns. Hence, the classical picture of electrons traversing the crystal as plane-like waves in the directions of the Bragg beams which historically stems from the X-ray diffraction picture, is in fact misleading.

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Ravikumar, V., R. P. Rodrigues, and V. P. Dravid. "Direct imaging of spatially varying potential and charge across internal interfaces in solids." Proceedings, annual meeting, Electron Microscopy Society of America 53 (August 13, 1995): 316–17. http://dx.doi.org/10.1017/s0424820100137951.

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The importance of spatially varying potential (and thus charge) across lattice discontinuities in solids has been recognized in many technologically important systems, especially those containing electrically active interfaces, e.g. electroceramics. The presence of spatially varying potential across electroceramic interfaces has been indirectly deduced and analyzed using predominantly bulk measurement techniques like I-V, C-V curves and impedance spectroscopy. Direct imaging of spatially varying electrostatic potential profile and determination of the sign, magnitude and spatial distribution of the associated interface- and space- charge (and therefore defect density) in electroceramics have remained elusive.We have utilized the technique of transmission high energy electron holography to directly image and quantify the electrostatic potential across grain boundaries (GBs) in SrTiO3, a functional electroceramic. The phase of the exit wave function at the GB region can be altered by : (i) variation in local mean inner potential (related to the change in density of atoms at the GB), (ii) differential diffraction conditions across the interface, (iii) change in the local specimen thickness and, (iv) presence of local electrostatic (electrical charge) and magnetic potential.

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Han, Karen F., John W. Sedat, and David A. Agard. "Image reconstruction using a focus series on thick biological specimens: TEM CTF correction." Proceedings, annual meeting, Electron Microscopy Society of America 51 (August 1, 1993): 558–59. http://dx.doi.org/10.1017/s0424820100148629.

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The primary project of our laboratory is the investigation of chromatin structure by three dimensional electron microscope tomography. Three dimensional tomography involves the reconstruction of an object by combining multiple projection views of the object at different tilt angles. There are two complications that give rise to an inaccurate representation in the image of the projected object mass density: 1) electron-specimen interactions, and 2) electron microscope lens aberrations. In our abstract, “Analysis of Electron-specimen Interactions of Thick Biological Specimens in Transmission Electron Microscopy at 200 keV” elsewhere in these proceedings, we investigated image formation at the level of electron-specimen interactions at 200 keV. We extrapolated that at 300 keV, there is still a significant amount of elastic scattering for thick (up to 0.7 microns) biological specimens . Here, we demonstrate that this allows the correction of the microscope aberration function through multiple focus observations can enhance contrast.For high resolution electron microscopy of crystalline materials, some authors have demonstrated that the focus variation method to reconstruct the specimen exit-surface electron wave can lead to an improvement in resolution.

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Cowley, J. M., and M. A. Gribelyuk. "High-resolution coherent imaging in STEM." Proceedings, annual meeting, Electron Microscopy Society of America 51 (August 1, 1993): 1082–83. http://dx.doi.org/10.1017/s0424820100151246.

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The ultimate aim of high resolution electron microscopy is the accurate determination of the positions and types of the atoms in a specimen. The coherent imaging theory for STEM is reviewed with the emphasis on its potential for achieving this aim by holographic methods. The STEM modes of holography are in many respects equivalent to the corresponding TEM modes, but have the advantage that, because with a FEG electron source the focussed probes have sub-nanometer diameter, a strong signal is obtained from the illuminated region and the problem of shot-noise is much less important.The original proposal for holography by Gabor envisaged the use of a reconstruction process on the recorded hologram to correct for the lens aberrations and hence improve the image resolution. The more general and more challenging problem is to reconstruct the aberration-free wave function at the exit face of the specimen (with its real and imaginary, or amplitude and phase, components) and then to invert the dynamical diffraction process and derive the projected potential distribution of the object.

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Journal articles on the topic 'Exit wave function'

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