11,950 research outputs found
A Novel Self-Intersection Penalty Term for Statistical Body Shape Models and Its Applications in 3D Pose Estimation
Statistical body shape models are widely used in 3D pose estimation due to
their low-dimensional parameters representation. However, it is difficult to
avoid self-intersection between body parts accurately. Motivated by this fact,
we proposed a novel self-intersection penalty term for statistical body shape
models applied in 3D pose estimation. To avoid the trouble of computing
self-intersection for complex surfaces like the body meshes, the gradient of
our proposed self-intersection penalty term is manually derived from the
perspective of geometry. First, the self-intersection penalty term is defined
as the volume of the self-intersection region. To calculate the partial
derivatives with respect to the coordinates of the vertices, we employed
detection rays to divide vertices of statistical body shape models into
different groups depending on whether the vertex is in the region of
self-intersection. Second, the partial derivatives could be easily derived by
the normal vectors of neighboring triangles of the vertices. Finally, this
penalty term could be applied in gradient-based optimization algorithms to
remove the self-intersection of triangular meshes without using any
approximation. Qualitative and quantitative evaluations were conducted to
demonstrate the effectiveness and generality of our proposed method compared
with previous approaches. The experimental results show that our proposed
penalty term can avoid self-intersection to exclude unreasonable predictions
and improves the accuracy of 3D pose estimation indirectly. Further more, the
proposed method could be employed universally in triangular mesh based 3D
reconstruction
Optimization on fixed low latency implementation of GBT protocol in FPGA
In the upgrade of ATLAS experiment, the front-end electronics components are
subjected to a large radiation background. Meanwhile high speed optical links
are required for the data transmission between the on-detector and off-detector
electronics. The GBT architecture and the Versatile Link (VL) project are
designed by CERN to support the 4.8 Gbps line rate bidirectional high-speed
data transmission which is called GBT link. In the ATLAS upgrade, besides the
link with on-detector, the GBT link is also used between different off-detector
systems. The GBTX ASIC is designed for the on-detector front-end,
correspondingly for the off-detector electronics, the GBT architecture is
implemented in Field Programmable Gate Arrays (FPGA). CERN launches the
GBT-FPGA project to provide examples in different types of FPGA. In the ATLAS
upgrade framework, the Front-End LInk eXchange (FELIX) system is used to
interface the front-end electronics of several ATLAS subsystems. The GBT link
is used between them, to transfer the detector data and the timing, trigger,
control and monitoring information. The trigger signal distributed in the
down-link from FELIX to the front-end requires a fixed and low latency. In this
paper, several optimizations on the GBT-FPGA IP core are introduced, to achieve
a lower fixed latency. For FELIX, a common firmware will be used to interface
different front-ends with support of both GBT modes: the forward error
correction mode and the wide mode. The modified GBT-FPGA core has the ability
to switch between the GBT modes without FPGA reprogramming. The system clock
distribution of the multi-channel FELIX firmware is also discussed in this
paper
Projected Density Matrix Embedding Theory with Applications to the Two-Dimensional Hubbard Model
Density matrix embedding theory (DMET) is a quantum embedding theory for
strongly correlated systems. From a computational perspective, one bottleneck
in DMET is the optimization of the correlation potential to achieve
self-consistency, especially for heterogeneous systems of large size. We
propose a new method, called projected density matrix embedding theory
(p-DMET), which achieves self-consistency without needing to optimize a
correlation potential. We demonstrate the performance of p-DMET on the
two-dimensional Hubbard model.Comment: 25 pages, 8 figure
Conditioning of BPM pickup signals for operations of the Duke storage ring with a wide range of single-bunch current
The Duke storage ring is a dedicated driver for the storage ring based
oscillator free-electron lasers (FELs), and the High Intensity Gamma-ray Source
(HIGS). It is operated with a beam current ranging from about 1 mA to 100 mA
per bunch for various operations and accelerator physics studies. High
performance operations of the FEL and gamma-ray source require a stable
electron beam orbit, which has been realized by the global orbit feedback
system. As a critical part of the orbit feedback system, the electron beam
position monitors (BPMs) are required to be able to precisely measure the
electron beam orbit in a wide range of the single-bunch current. However, the
high peak voltage of the BPM pickups associated with high single-bunch current
degrades the performance of the BPM electronics, and can potentially damage the
BPM electronics. A signal conditioning method using low pass filters is
developed to reduce the peak voltage to protect the BPM electronics, and to
make the BPMs capable of working with a wide range of single-bunch current.
Simulations and electron beam based tests are performed. The results show that
the Duke storage ring BPM system is capable of providing precise orbit
measurements to ensure highly stable FEL and HIGS operations
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