3,665 research outputs found
Three-dimensional Lagrangian Voronoi analysis for clustering of particles and bubbles in turbulence
Three-dimensional Voronoi analysis is used to quantify the clustering of
inertial particles in homogeneous isotropic turbulence using data from numerics
and experiments. We study the clustering behavior at different density ratios
and particle response times (i.e. Stokes numbers St). The Probability Density
Functions (PDFs) of the Voronoi cell volumes of light and heavy particles show
a different behavior from that of randomly distributed particles -i.e. fluid
tracers-implying that clustering is present. The standard deviation of the PDF
normalized by that of randomly distributed particles is used to quantify the
clustering. Light particles show maximum clustering for St around 1-2. The
results are consistent with previous investigations employing other approaches
to quantify the clustering. We also present the joint PDFs of enstrophy and
Voronoi volumes and their Lagrangian autocorrelations. The small Voronoi
volumes of light particles correspond to regions of higher enstrophy than those
of heavy particles, indicating that light particles cluster in higher vorticity
regions. The Lagrangian temporal autocorrelation function of Voronoi volumes
shows that the clustering of light particles lasts much longer than that of
heavy or neutrally buoyant particles. Due to inertial effects, the Lagrangian
autocorrelation time-scale of clustered light particles is even longer than
that of the enstrophy of the flow itself.Comment: J. Fluid Mech. 201
Making Infrastructure Procurement Processes more Flexible under Uncertainty
A third to a half of development projects undergo restructuring due to changes in project objectives, scope or other unanticipated changes, therefore requiring schedule extensions, budget additions and rework. Current procurement processes discourage managers from responding strategically by anticipating and preparing for such changes in advance through better information search and design concept evaluation. This paper suggests three principles for making the front-end phases of procurement more flexible - understanding uncertainty, studying system-wide impacts, and phasing designs. A case study analysis of urban water system design in Kabul demonstrates the conceptual and analytical application of these principles
Impact of parameter variations on circuits and microarchitecture
Parameter variations, which are increasing along with advances in process technologies, affect both timing and power. Variability must be considered at both the circuit and microarchitectural design levels to keep pace with performance scaling and to keep power consumption within reasonable limits. This article presents an overview of the main sources of variability and surveys variation-tolerant circuit and microarchitectural approaches.Peer ReviewedPostprint (published version
Evanescent field optical readout of graphene mechanical motion at room temperature
Graphene mechanical resonators have recently attracted considerable attention
for use in precision force and mass sensing applications. To date, readout of
their oscillatory motion has typically required cryogenic conditions to achieve
high sensitivity, restricting their range of applications. Here we report the
first demonstration of evanescent optical readout of graphene motion, using a
scheme which does not require cryogenic conditions and exhibits enhanced
sensitivity and bandwidth at room temperature. We utilise a high
microsphere to enable evanescent readout of a 70 m diameter graphene drum
resonator with a signal-to-noise ratio of greater than 25 dB, corresponding to
a transduction sensitivity of 2.6 m
. The sensitivity of force measurements using this
resonator is limited by the thermal noise driving the resonator, corresponding
to a force sensitivity of N
with a bandwidth of 35 kHz at room temperature (T = 300
K). Measurements on a 30 m graphene drum had sufficient sensitivity to
resolve the lowest three thermally driven mechanical resonances.Comment: Fixed formatting errors in bibliograph
The Virtual Block Interface: A Flexible Alternative to the Conventional Virtual Memory Framework
Computers continue to diversify with respect to system designs, emerging
memory technologies, and application memory demands. Unfortunately, continually
adapting the conventional virtual memory framework to each possible system
configuration is challenging, and often results in performance loss or requires
non-trivial workarounds. To address these challenges, we propose a new virtual
memory framework, the Virtual Block Interface (VBI). We design VBI based on the
key idea that delegating memory management duties to hardware can reduce the
overheads and software complexity associated with virtual memory. VBI
introduces a set of variable-sized virtual blocks (VBs) to applications. Each
VB is a contiguous region of the globally-visible VBI address space, and an
application can allocate each semantically meaningful unit of information
(e.g., a data structure) in a separate VB. VBI decouples access protection from
memory allocation and address translation. While the OS controls which programs
have access to which VBs, dedicated hardware in the memory controller manages
the physical memory allocation and address translation of the VBs. This
approach enables several architectural optimizations to (1) efficiently and
flexibly cater to different and increasingly diverse system configurations, and
(2) eliminate key inefficiencies of conventional virtual memory. We demonstrate
the benefits of VBI with two important use cases: (1) reducing the overheads of
address translation (for both native execution and virtual machine
environments), as VBI reduces the number of translation requests and associated
memory accesses; and (2) two heterogeneous main memory architectures, where VBI
increases the effectiveness of managing fast memory regions. For both cases,
VBI significanttly improves performance over conventional virtual memory
MarkerMiner 1.0: a new application for phylogenetic marker development using angiosperm transcriptomes
Premise of the study: Targeted sequencing using next-generation sequencing (NGS) platforms offers enormous potential for plant systematics by enabling economical acquisition of multilocus data sets that can resolve difficult phylogenetic problems. However, because discovery of single-copy nuclear (SCN) loci from NGS data requires both bioinformatics skills and access to high-performance computing resources, the application of NGS data has been limited.
Methods and Results: We developed MarkerMiner 1.0, a fully automated, open-access bioinformatic workflow and application for discovery of SCN loci in angiosperms. Our new tool identified as many as 1993 SCN loci from transcriptomic data sampled as part of four independent test cases representing marker development projects at different phylogenetic scales.
Conclusions: MarkerMiner is an easy-to-use and effective tool for discovery of putative SCN loci. It can be run locally or via the Web, and its tabular and alignment outputs facilitate efficient downstream assessments of phylogenetic utility, locus selection, intron-exon boundary prediction, and primer or probe development
Unique in the shopping mall: On the reidentifiability of credit card metadata
Large-scale data sets of human behavior have the potential to fundamentally transform the way we fight diseases, design cities, or perform research. Metadata, however, contain sensitive information. Understanding the privacy of these data sets is key to their broad use and, ultimately, their impact. We study 3 months of credit card records for 1.1 million people and show that four spatiotemporal points are enough to uniquely reidentify 90% of individuals. We show that knowing the price of a transaction increases the risk of reidentification by 22%, on average. Finally, we show that even data sets that provide coarse information at any or all of the dimensions provide little anonymity and that women are more reidentifiable than men in credit card metadata.European Commission. Framework Programme 7 (Marie Curie Action. Grant 264994)U.S. Army Research Laboratory (Cooperative Agreement W911NF-09-2-0053)Belgian American Educational Foundation, inc.Wallonie-Bruxelles Internationa
Electronic structure of Pr2MnNiO6 from x-ray photoemission, absorption and density functional theory
The electronic structure of double perovskite Pr2MnNiO6 is studied using core
x-ray photoelectron spectroscopy and x-ray absorption spectroscopy. The 2p
x-ray absorption spectra show that Mn and Ni are in 2+ and 4+ states
respectively. Using charge transfer multiplet analysis of Ni and Mn 2p XPS
spectra, we find charge transfer energies {\Delta} of 3.5 and 2.5 eV for Ni and
Mn respectively. The ground state of Ni2+ and Mn4+ reveal a higher d electron
count of 8.21 and 3.38 respectively as compared to the atomic values of 8.00
and 3.00 respectively thereby indicating the covalent nature of the system. The
O 1s edge absorption spectra reveal a band gap of 0.9 eV which is comparable to
the value obtained from first principle calculations for U-J >= 2 eV. The
density of states clearly reveal a strong p-d type charge transfer character of
the system, with band gap proportional to average charge transfer energy of
Ni2+ and Mn4+ ions.Comment: 18 pages, 9 figure
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