307 research outputs found
Laser-Cooled Ion Beams and Strongly Coupled Plasmas for Precision Experiments
The first part of this thesis summarizes the results of laser-cooling of relativistic C3+ ion beams at the ESR/GSI. It is shown that laser cooling at high beam energies is feasible and that momentum spreads much smaller than those observed for electron cooling can be achieved. Resulty indicate that space-charge dominated beams have been observed, reaching the regime of strong coupling which is an essential prerequisite for beam crystallization. Moderate electron cooling was employed to create three-dimensionally cold beams. With the laser cooled beams it was possible to perform precision VUV spectroscopy of the cooling transition.
In the second part results on large-scale realistic simulations on the stopping of highly charged ions in a laser-cooled one-component plasma of 24Mg+ ions confined in a harmonic potential are presented. It is shown that cooling times short enough for cooling unstable nuclei can be achieved and fast recooling of the plasma is possible. With this cooling scheme highly charged ions for precision experiments such as mass spectrometry in Penning traps at millikelvin temperatures can be delivered
Tuning and optimization for a variety of many-core architectures without changing a single line of implementation code using the Alpaka library
We present an analysis on optimizing performance of a single C++11 source
code using the Alpaka hardware abstraction library. For this we use the general
matrix multiplication (GEMM) algorithm in order to show that compilers can
optimize Alpaka code effectively when tuning key parameters of the algorithm.
We do not intend to rival existing, highly optimized DGEMM versions, but merely
choose this example to prove that Alpaka allows for platform-specific tuning
with a single source code. In addition we analyze the optimization potential
available with vendor-specific compilers when confronted with the heavily
templated abstractions of Alpaka. We specifically test the code for bleeding
edge architectures such as Nvidia's Tesla P100, Intel's Knights Landing (KNL)
and Haswell architecture as well as IBM's Power8 system. On some of these we
are able to reach almost 50\% of the peak floating point operation performance
using the aforementioned means. When adding compiler-specific #pragmas we are
able to reach 5 TFLOPS/s on a P100 and over 1 TFLOPS/s on a KNL system.Comment: Accepted paper for the P\^{}3MA workshop at the ISC 2017 in Frankfur
Quantitatively consistent computation of coherent and incoherent radiation in particle-in-cell codes - a general form factor formalism for macro-particles
Quantitative predictions from synthetic radiation diagnostics often have to
consider all accelerated particles. For particle-in-cell (PIC) codes, this not
only means including all macro-particles but also taking into account the
discrete electron distribution associated with them. This paper presents a
general form factor formalism that allows to determine the radiation from this
discrete electron distribution in order to compute the coherent and incoherent
radiation self-consistently. Furthermore, we discuss a memory-efficient
implementation that allows PIC simulations with billions of macro-particles.
The impact on the radiation spectra is demonstrated on a large scale LWFA
simulation.Comment: Proceedings of the EAAC 2017, This manuscript version is made
available under the CC-BY-NC-ND 4.0 licens
Dosimetric evidence confirms computational model for magnetic field induced dose distortions of therapeutic proton beams
Given the sensitivity of proton therapy to anatomical variations, this cancer
treatment modality is expected to benefit greatly from integration with
magnetic resonance (MR) imaging. One of the obstacles hindering such an
integration are strong magnetic field induced dose distortions. These have been
predicted in simulation studies, but no experimental validation has been
performed so far. Here we show the first measurement of planar distributions of
dose deposited by therapeutic proton pencil beams traversing a one-Tesla
transversal magnetic field while depositing energy in a tissue-like phantom
using film dosimetry. The lateral beam deflection ranges from one millimeter to
one centimeter for 80 to 180 MeV beams. Simulated and measured deflection agree
within one millimeter for all studied energies. These results proof that the
magnetic field induced proton beam deflection is both measurable and accurately
predictable. This demonstrates the feasibility of accurate dose measurement and
hence validates dose predictions for the framework of MR-integrated proton
therapy
On the Scalability of Data Reduction Techniques in Current and Upcoming HPC Systems from an Application Perspective
We implement and benchmark parallel I/O methods for the fully-manycore driven
particle-in-cell code PIConGPU. Identifying throughput and overall I/O size as
a major challenge for applications on today's and future HPC systems, we
present a scaling law characterizing performance bottlenecks in
state-of-the-art approaches for data reduction. Consequently, we propose,
implement and verify multi-threaded data-transformations for the I/O library
ADIOS as a feasible way to trade underutilized host-side compute potential on
heterogeneous systems for reduced I/O latency.Comment: 15 pages, 5 figures, accepted for DRBSD-1 in conjunction with ISC'1
A Deep Dive into Machine Learning Density Functional Theory for Materials Science and Chemistry
With the growth of computational resources, the scope of electronic structure
simulations has increased greatly. Artificial intelligence and robust data
analysis hold the promise to accelerate large-scale simulations and their
analysis to hitherto unattainable scales. Machine learning is a rapidly growing
field for the processing of such complex datasets. It has recently gained
traction in the domain of electronic structure simulations, where density
functional theory takes the prominent role of the most widely used electronic
structure method. Thus, DFT calculations represent one of the largest loads on
academic high-performance computing systems across the world. Accelerating
these with machine learning can reduce the resources required and enables
simulations of larger systems. Hence, the combination of density functional
theory and machine learning has the potential to rapidly advance electronic
structure applications such as in-silico materials discovery and the search for
new chemical reaction pathways. We provide the theoretical background of both
density functional theory and machine learning on a generally accessible level.
This serves as the basis of our comprehensive review including research
articles up to December 2020 in chemistry and materials science that employ
machine-learning techniques. In our analysis, we categorize the body of
research into main threads and extract impactful results. We conclude our
review with an outlook on exciting research directions in terms of a citation
analysis
Flying Adversarial Patches: Manipulating the Behavior of Deep Learning-based Autonomous Multirotors
Autonomous flying robots, e.g. multirotors, often rely on a neural network
that makes predictions based on a camera image. These deep learning (DL) models
can compute surprising results if applied to input images outside the training
domain. Adversarial attacks exploit this fault, for example, by computing small
images, so-called adversarial patches, that can be placed in the environment to
manipulate the neural network's prediction. We introduce flying adversarial
patches, where an image is mounted on another flying robot and therefore can be
placed anywhere in the field of view of a victim multirotor. For an effective
attack, we compare three methods that simultaneously optimize the adversarial
patch and its position in the input image. We perform an empirical validation
on a publicly available DL model and dataset for autonomous multirotors.
Ultimately, our attacking multirotor would be able to gain full control over
the motions of the victim multirotor.Comment: 6 pages, 5 figures, Workshop on Multi-Robot Learning, International
Conference on Robotics and Automation (ICRA
- âŚ