The Technique Of Point Projection Spectroscopy And Its Application To The Planar Foil Mix Experiment At The AWE HELEN Laser

1989 ◽  
Author(s):  
P. A. Rosen ◽  
P. Fieldhouse ◽  
J. C. V. Hansom ◽  
K. Oades ◽  
T. J. Goldsack ◽  
...  
Keyword(s):  
Projection Spectroscopy ◽  
Point Projection

Low-energy point-reflection EM

1995 ◽  
Vol 53 ◽  
pp. 610-611
Author(s):  
J. C. H. Spence ◽  
X. Zhang ◽  
J. M. Zuo ◽  
U. Weierstall ◽  
E. Munro ◽  
...  
Keyword(s):  
Low Voltage ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Experimental Point ◽  
Crystalline Substrate ◽  
Point Reflection ◽  
Reflection Geometry ◽  
Optical Analog ◽  
Point Projection ◽  
Atomically Flat

The limited penetration of the low-voltage point-projection microscope (PPM) may be avoided by using the reflection geometry to image clean surfaces in ultra-high vacuum. Figure 1 shows the geometry we are using for experimental point-reflection (PRM) imaging. A nanotip field-emitter at about 100 - 1000 volts is placed above a grounded atomically flat crystalline substrate, which acts as a mirror and anode. Since most of the potential is dropped very close to the tip, trajectories are reasonably straight if the sample is in the far-field of the tip. A resolution of 10 nm is sought initially. The specular divergent RHEED beam then defines a virtual source S' below the surface, resulting in an equivalent arrangement to PPM (or defocused CBED). Shadow images of surface asperities are then expected on the distant detector, out of focus by the tip-to-sample distance. These images can be interpreted as in-line electron holograms and so reconstructed (see X. Zhang et al, these proceedings). Optical analog experiments confirm the absence of foreshortening when the detector is parallel to the surface.

Fresnel interference in point-projection imaging of purple membrane

1995 ◽  
Vol 53 ◽  
pp. 846-847
Author(s):  
X. Zhang ◽  
J. Spence ◽  
W. Qian ◽  
D. Taylor ◽  
K. Taylor
Keyword(s):  
Detection Efficiency ◽  
Mean Free Path ◽  
Purple Membrane ◽  
Unit Cell Dimension ◽  
Experimental Point ◽  
Membrane Thickness ◽  
Low Energies ◽  
Channel Plate ◽  
Point Projection ◽  
Inelastic Mean Free Path

Experimental point-projection shadow microscope (PPM) images of uncoated, unstained purple membrane (PM, bacteriorhodopsin, a membrane protein from Halobacterium holobium) were obtained recently using 100 volt electrons. The membrane thickness is about 5 nm and the hexagonal unit cell dimension 6 nm. The images show contrast around the edges of small holes, as shown in figure 1. The interior of the film is opaque. Since the inelastic mean free path for 100V electrons in carbon (about 6 Å) is much less than the sample thickness, the question arises that how much, if any, transmission of elastically scattered electrons occurs. A large inelastic contribution is also expected, attenuated by the reduced detection efficiency of the channel plate at low energies. Quantitative experiments using an energy-loss spectrometer are planned. Recently Shedd has shown that at about 100V contrast in PPM images of thin gold films can be explained as Fresnel interference effects between different pinholes in the film, separated by less than the coherence width.

scholarly journals A torus patch approximation approach for point projection on surfaces

2009 ◽  
Vol 26 (5) ◽  
pp. 593-598 ◽  
Author(s):  
Xiao-Ming Liu ◽  
Lei Yang ◽  
Jun-Hai Yong ◽  
He-Jin Gu ◽  
Jia-Guang Sun
Keyword(s):  
Approximation Approach ◽  
Point Projection

A Torus Patch Approximation Approach for Point Projection on Implicit Surfaces

2011 ◽  
Vol 346 ◽  
pp. 259-265
Author(s):  
Xiao Ming Liu ◽  
Lei Yang ◽  
Qiang Hu ◽  
Jun Hai Yong
Keyword(s):  
Iterative Algorithm ◽  
Geometric Modeling ◽  
Second Order ◽  
Implicit Surfaces ◽  
Implicit Surface ◽  
Approximation Approach ◽  
Initial Values ◽  
Point Projection

Point projection on an implicit surface is essential for the geometric modeling and graphics applications of it. This paper presents a method for computing the principle curvatures and principle directions of an implicit surface. Using the principle curvatures and principle directions, we construct a torus patch to approximate the implicit surface locally. The torus patch is second order osculating to the implicit surface. By taking advantage of the approximation torus patch, this paper develops a second order geometric iterative algorithm for point projection on the implicit surface. Experiments illustrate the efficiency and less dependency on initial values of our algorithm.

Importance Point Projection for GPU-based Final Gathering

2011 ◽  
Vol 30 (4) ◽  
pp. 1327-1336 ◽  
Author(s):  
David Maletz ◽  
Rui Wang
Keyword(s):  
Final Gathering ◽  
Point Projection

scholarly journals Short pulse, high resolution, backlighters for point projection high-energy radiography at the National Ignition Facility

2017 ◽  
Vol 24 (5) ◽  
pp. 053104 ◽  
Author(s):  
R. Tommasini ◽  
C. Bailey ◽  
D. K. Bradley ◽  
M. Bowers ◽  
H. Chen ◽  
...  
Keyword(s):  
High Resolution ◽  
Short Pulse ◽  
High Energy ◽  
National Ignition Facility ◽  
Point Projection

scholarly journals Numerical Algorithms for Simulation of a Fluid-Filed Fracture Evolution in a Poroelastic Medium

2021 ◽  
pp. 24-35
Author(s):  
V. E Borisov ◽  
A. V Ivanov ◽  
B. V Kritsky ◽  
E. B Savenkov
Keyword(s):  
Finite Element ◽  
Fluid Flow ◽  
Geometric Model ◽  
Numerical Algorithms ◽  
Problem Solution ◽  
Poroelastic Medium ◽  
Heterogeneous Distribution ◽  
Coupled Problem ◽  
Fracture Evolution ◽  
Point Projection

The paper deals with the computational framework for the numerical simulation of the three dimensional fluid-filled fracture evolution in a poroelastic medium. The model consists of several groups of equations including the Biot poroelastic model to describe a bulk medium behavior, Reynold’s lubrication equations to describe a flow inside fracture and corresponding bulk/fracture interface conditions. The geometric model of the fracture assumes that it is described as an arbitrary sufficiently smooth surface with a boundary. Main attention is paid to describing numerical algorithms for particular problems (poroelasticity, fracture fluid flow, fracture evolution) as well as an algorithm for the coupled problem solution. An implicit fracture mid-surface representation approach based on the closest point projection operator is a particular feature of the proposed algorithms. Such a representation is used to describe the fracture mid-surface in the poroelastic solver, Reynold’s lubrication equation solver and for simulation of fracture evolutions. The poroelastic solver is based on a special variant of X-FEM algorithms, which uses the closest point representation of the fracture. To solve Reynold’s lubrication equations, which model the fluid flow in fracture, a finite element version of the closet point projection method for PDEs surface is used. As a result, the algorithm for the coupled problem is purely Eulerian and uses the same finite element mesh to solve equations defined in the bulk and on the fracture mid-surface. Finally, we present results of the numerical simulations which demonstrate possibilities of the proposed numerical techniques, in particular, a problem in a media with a heterogeneous distribution of transport, elastic and toughness properties.

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