58 research outputs found
Developable Quad Meshes
There are different ways to capture the property of a surface being
developable, i.e., it can be mapped to a planar domain without stretching or
tearing. Contributions range from special parametrizations to
discrete-isometric mappings. So far, a local criterion expressing the
developability of general quad meshes has been lacking. In this paper, we
propose a new and efficient discrete developability criterion that is based on
a property well-known from differential geometry, namely a rank-deficient
second fundamental form. This criterion is expressed in terms of the canonical
checkerboard patterns inscribed in a quad mesh which already was successful in
describing discrete-isometric mappings. In combination with standard global
optimization procedures, we are able to perform developable lofting,
approximation, and design. The meshes we employ are combinatorially regular
quad meshes with isolated singularities but are otherwise not required to
follow any special curves. They are thus easily embedded into a design workflow
involving standard operations like re-meshing, trimming, and merging
operations
Computational Design of Cold Bent Glass Fa\c{c}ades
Cold bent glass is a promising and cost-efficient method for realizing doubly
curved glass fa\c{c}ades. They are produced by attaching planar glass sheets to
curved frames and require keeping the occurring stress within safe limits.
However, it is very challenging to navigate the design space of cold bent glass
panels due to the fragility of the material, which impedes the form-finding for
practically feasible and aesthetically pleasing cold bent glass fa\c{c}ades. We
propose an interactive, data-driven approach for designing cold bent glass
fa\c{c}ades that can be seamlessly integrated into a typical architectural
design pipeline. Our method allows non-expert users to interactively edit a
parametric surface while providing real-time feedback on the deformed shape and
maximum stress of cold bent glass panels. Designs are automatically refined to
minimize several fairness criteria while maximal stresses are kept within glass
limits. We achieve interactive frame rates by using a differentiable Mixture
Density Network trained from more than a million simulations. Given a curved
boundary, our regression model is capable of handling multistable
configurations and accurately predicting the equilibrium shape of the panel and
its corresponding maximal stress. We show predictions are highly accurate and
validate our results with a physical realization of a cold bent glass surface
Kinematically complete experimental study of Compton scattering at helium atoms near the ionization threshold
Compton scattering is one of the fundamental interaction processes of light
with matter. Already upon its discovery [1] it was described as a billiard-type
collision of a photon kicking a quasi-free electron. With decreasing photon
energy, the maximum possible momentum transfer becomes so small that the
corresponding energy falls below the binding energy of the electron. Then
ionization by Compton scattering becomes an intriguing quantum phenomenon. Here
we report a kinematically complete experiment on Compton scattering at helium
atoms below that threshold. We determine the momentum correlations of the
electron, the recoiling ion, and the scattered photon in a coincidence
experiment finding that electrons are not only emitted in the direction of the
momentum transfer, but that there is a second peak of ejection to the backward
direction. This finding links Compton scattering to processes as ionization by
ultrashort optical pulses [2], electron impact ionization [3,4], ion impact
ionization [5,6], and neutron scattering [7] where similar momentum patterns
occur.Comment: 7 pages, 4 figure
Observation of enhanced chiral asymmetries in the inner-shell photoionization of uniaxially oriented methyloxirane enantiomers
Most large molecules are chiral in their structure: they exist as two
enantiomers, which are mirror images of each other. Whereas the rovibronic
sublevels of two enantiomers are almost identical, it turns out that the
photoelectric effect is sensitive to the absolute configuration of the ionized
enantiomer - an effect termed Photoelectron Circular Dichroism (PECD). Our
comprehensive study demonstrates that the origin of PECD can be found in the
molecular frame electron emission pattern connecting PECD to other fundamental
photophysical effects as the circular dichroism in angular distributions
(CDAD). Accordingly, orienting a chiral molecule in space enhances the PECD by
a factor of about 10
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