237 research outputs found
Accelerating Foreign-Key Joins using Asymmetric Memory Channels
Indexed Foreign-Key Joins expose a very asymmetric access
pattern: the Foreign-Key Index is sequentially scanned
whilst the Primary-Key table is target of many quasi-random
lookups which is the dominant cost factor. To reduce the
costs of the random lookups the fact-table can be (re-) partitioned
at runtime to increase access locality on the dimension
table, and thus limit the random memory access to
inside the CPU's cache. However, this is very hard to optimize
and the performance impact on recent architectures is
limited because the partitioning costs consume most of the
achievable join improvement.
GPGPUs on the other hand have an architecture that is
well suited for this operation: a relatively slow connection to
the large system memory and a very fast connection to the
smaller internal device memory. We show how to accelerate
Foreign-Key Joins by executing the random table lookups on
the GPU's VRAM while sequentially streaming the Foreign-
Key-Index through the PCI-E Bus. We also experimentally
study the memory access costs on GPU and CPU to provide
estimations of the benefit of this technique
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Energy Flux Characterisation of Atmospheric Pressure Plasma Spray Torches with Passive Thermal Probes
Passive thermal probes were applied on two different plasma spraying devices to gain a detailed understanding of the energy flux towards the substrate under atmospheric pressure. The challenge of very high thermal load was solved by using an advanced time-resolved measuring and evaluation technique. The combination with a controlled movement of the jets allowed to obtain insightful radial profiles. The energy flux to the substrate changes linearly to the electrical input power. When adding diatomic gases (H2/N2) to the gas mixture the energy flux increases significantly, suggesting a more efficient energy transport. For increasing the axial distance, the energy flux shows a quadratic reduction. The obtained radial profiles are exemplarily utilized to show the inhomogeneous effect of powder injection on the energy flux distribution
X-Device Query Processing by Bitwise Distribution
The diversity of hardware components within a single system calls for strategies for efficient cross-device data processing. For exam- ple, existing approaches to CPU/GPU co-processing distribute individual relational operators to the “most appropriate” device. While pleasantly simple, this strategy has a number of problems: it may leave the “inappropriate” devices idle while overloading the “appropriate” device and putting a high pressure on the PCI bus. To address these issues we distribute data among the devices by par- tially decomposing relations at the granularity of individual bits. Each of the resulting bit-partitions is stored and processed on one of the available devices. Using this strategy, we implemented a processor for spatial range queries that makes efficient use of all available devices. The performance gains achieved indicate that bitwise distribution makes a good cross-device processing strategy
In Situ Laser Light Scattering for Temporally and Locally Resolved Studies on Nanoparticle Trapping in a Gas Aggregation Source
Gas phase synthesis of nanoparticles (NPs) via magnetron sputtering in a gas aggregation source (GAS) has become a well-established method since its conceptualization three decades ago. NP formation is commonly described in terms of nucleation, growth, and transport alongside the gas stream. However, the NP formation and transport involve complex non-equilibrium processes, which are still the subject of investigation. The development of in situ investigation techniques such as UV–Vis spectroscopy and small angle X-ray scattering enabled further insights into the dynamic processes inside the GAS and have recently revealed NP trapping at different distances from the magnetron source. The main drawback of these techniques is their limited spatial resolution. To understand the spatio-temporal behavior of NP trapping, an in situ laser light scattering technique is applied in this study. By this approach, silver NPs are made visible inside the GAS with good spatial and temporal resolution. It is found that the argon gas pressure, as well as different gas inlet configurations, have a strong impact on the trapping behavior of NPs inside the GAS. The different gas inlet configurations not only affect the trapping of NPs, but also the size distribution and deposition rate of NPs
A High Order Method for Contour Integrals with an Application to Plasma Modeling in Nuclear Fusion
We introduce a novel method to compute approximations of contour integrals.The new method is based on the coarea formula in combination with a Galerkin projection.As such it fits seamlessly into the spirit of hp/spectral finite element methods and circumvents the expensive and technical computation of contours.We provide convergence estimates showing that high order convergence can be achieved provided the data is sufficiently smooth.The theoretical results are supplemented by extensive numerical experiments for an example application from plasma modeling in nuclear fusion
Instant-on scientific data warehouses: Lazy ETL for data-intensive research
In the dawning era of data intensive research, scientific discovery deploys data analysis techniques similar to those that drive business intelligence. Similar to classical Extract, Transform and Load (ETL) processes, data is loaded entirely from external data sources (repositories) into a scientific data warehouse before it can be analyzed. This process is both, time and resource intensive and may not be entirely necessary if only a subset of the data is of interest to a particular user. To overcome this problem, we propose a novel technique to lower the costs for data loading: Lazy ETL. Data is extracted and loaded transparently on-the-fly only for the required data items. Extensive experiments demonstrate the significant reduction of the time from source data availability to query answer compared to state-of-the-art solutions. In addition to reducing the costs for bootstrapping a scientific data warehouse, our approach also reduces the costs for loading new incoming data
X-device query processing by bitwise distribution
htmlabstractThe diversity of hardware components within a single system calls for strategies for efficient cross-device data processing. For exam- ple, existing approaches to CPU/GPU co-processing distribute individual relational operators to the “most appropriate” device. While pleasantly simple, this strategy has a number of problems: it may leave the “inappropriate” devices idle while overloading the “appropriate” device and putting a high pressure on the PCI bus. To address these issues we distribute data among the devices by par- tially decomposing relations at the granularity of individual bits. Each of the resulting bit-partitions is stored and processed on one of the available devices. Using this strategy, we implemented a processor for spatial range queries that makes efficient use of all available devices. The performance gains achieved indicate that bitwise distribution makes a good cross-device processing strategy
Relationship Between Microbial Growth and Hydraulic Properties at the Sub-Pore Scale
Accumulation of microbial biomass and its influence on porous media flow were investigated under saturated flow conditions. Microfluidic experiments were performed with model organisms, and their accumulation was observed in the pore space and on the sub-pore scale. Time-lapse optical imaging revealed different modes of biomass accumulation through primary colonization, secondary growth, and filtration events, showing the formation of preferential flow pathways in the flooding domain as result of the increasing interstitial velocity. Navier–Stokes–Brinkmann flow simulations were performed on the segmented images—a digital-twin approach—considering locally accumulated biomass as impermeable or permeable based on optical biomass density. By comparing simulation results and the experimental responses, it was shown that accumulated biomass can be considered as a permeable medium. The average intra-biomass permeability was determined to be 500 ± 200 mD, which is more than a factor of 10 larger than previously assumed in modeling studies. These findings have substantial consequences: (1) a remaining interstitial permeability, as a result of the observed channel formation and the intra-biomass permeability, and (2) a potential advective nutrient supply, which can be considered more efficient than a purely diffusive supply. The second point may lead to higher metabolic activity and substrate conversion rates which is of particular interest for geobiotechnological applications.publishedVersio
On the plasma permeability of highly porous ceramic framework materials using polymers as marker materials
Highly porous framework materials are of large interest due to their broad potential for application, for example, as sensors or catalysts. A new approach is presented to investigate, how deep plasma species can penetrate such materials. For this purpose, a polymer (ethylene propylene diene monomere rubber) is used as marker material and covered with the porous material during plasma exposure. Water contact-angle and X-ray photoelectron spectroscopy measurements are used to identify changes in the polymer surface, originating from the interaction of plasma species with the polymer. The method is demonstrated by studying the plasma permeability of tetrapodal zinc oxide framework materials with a porosity of about 90% in an oxygen low-pressure capacitively coupled plasma. Significant differences in the penetration depth ranging from roughly 1.6–4 mm are found for different densities of the material and different treatment conditions
Improved Long‐Term Stability and Reduced Humidity Effect in Gas Sensing: SiO 2 Ultra‐Thin Layered ZnO Columnar Films
The undoped and metal-doped zinc oxide columnar films (ZnO:Sn, ZnO:Fe, ZnO:Ag, and ZnO:Cu) are covered with an ultra-thin layer of SiO2 (10–20 nm). The electrical, UV, and volatile organic compounds (VOCs) sensing properties are evaluated under different ambient conditions for ≈7 months to investigate the impact of the top SiO2-layer on the long-term stability of samples. The obtained results show a high immunity of sensing properties of SiO2-coated samples to humidity. Furthermore, gas sensing measurements show that the loss in response after 203 days is significantly lower for coated samples indicating higher stability of sensing performance. For ZnO:Fe the gas response is reduced by about 90% after 203 days, but for SiO2-coated ZnO:Fe columnar films the gas response is slightly reduced by only 38%. The density functional theory (DFT) calculations show that water species bind strongly with the surface SiO2 layer atoms with a −0.129 e− charge transfer, which is, much higher compared to the interaction with ethanol and acetone. Calculations show strong binding of water species on the SiO2 layer indicating preferential absorption of water molecules on SiO2. The obtained results demonstrate an important role of the top SiO2 ultra-thin layer in order to produce humidity-tolerant sensitive devices
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