14,521 research outputs found
Parallel String Sample Sort
We discuss how string sorting algorithms can be parallelized on modern
multi-core shared memory machines. As a synthesis of the best sequential string
sorting algorithms and successful parallel sorting algorithms for atomic
objects, we propose string sample sort. The algorithm makes effective use of
the memory hierarchy, uses additional word level parallelism, and largely
avoids branch mispredictions. Additionally, we parallelize variants of multikey
quicksort and radix sort that are also useful in certain situations.Comment: 34 pages, 7 figures and 12 table
Modeling the Field Emission Current Fluctuation in Carbon Nanotube Thin Films
Owing to their distinct properties, carbon nanotubes (CNTs) have emerged as
promising candidate for field emission devices. It has been found
experimentally that the results related to the field emission performance show
variability. The design of an efficient field emitting device requires the
analysis of the variabilities with a systematic and multiphysics based modeling
approach. In this paper, we develop a model of randomly oriented CNTs in a thin
film by coupling the field emission phenomena, the electron-phonon transport
and the mechanics of single isolated CNT. A computational scheme is developed
by which the states of CNTs are updated in time incremental manner. The device
current is calculated by using Fowler-Nordheim equation for field emission to
study the performance at the device scale.Comment: 4 pages, 5 figure
Digital flight control research
The results of studies which were undertaken to contribute to the design of digital flight control systems, particularly for transport aircraft are presented. In addition to the overall design considerations for a digital flight control system, the following topics are discussed in detail: (1) aircraft attitude reference system design, (2) the digital computer configuration, (3) the design of a typical digital autopilot for transport aircraft, and (4) a hybrid flight simulator
Flux estimates of isoprene, methanol and acetone from airborne PTR-MS measurements over the tropical rainforest during the GABRIEL 2005 campaign
Tropical forests are a strong source of biogenic volatile organic compounds (BVOCs) to the atmosphere which can potentially impact the atmospheric oxidation capacity. Here we present airborne and ground-based BVOC measurements representative for the long dry season covering a large area of the northern Amazonian rainforest (6-3° N, 50-59° W). The measurements were conducted during the October 2005 GABRIEL (Guyanas Atmosphere-Biosphere exchange and Radicals Intensive Experiment with the Learjet) campaign. The vertical (35 m to 10 km) and diurnal (09:00-16:00) profiles of isoprene, its oxidation products methacrolein and methyl vinyl ketone and methanol and acetone, measured by PTR-MS (Proton Transfer Reaction Mass Spectrometry), have been used to empirically estimate their emission fluxes from the forest canopy on a regional scale. The mixed layer isoprene emission flux, inferred from the airborne measurements above 300 m, is 5.7 mg isoprene m-2 h-1 after compensating for chemistry and ~6.9 mg isoprene m-2 h-1 taking detrainment into account. This surface flux is in general agreement with previous tropical forest studies. Inferred methanol and acetone emission fluxes are 0.5 mg methanol m¿2 h¿1 and 0.35 mg acetone m-2 h-1, respectively. The BVOC measurements were compared with fluxes and mixing ratios simulated with a single-column chemistry and climate model (SCM). The inferred isoprene flux is substantially smaller than that simulated with an implementation of a commonly applied BVOC emission algorithm in the SCM
ShapeFit and ShapeKick for Robust, Scalable Structure from Motion
We introduce a new method for location recovery from pair-wise directions
that leverages an efficient convex program that comes with exact recovery
guarantees, even in the presence of adversarial outliers. When pairwise
directions represent scaled relative positions between pairs of views
(estimated for instance with epipolar geometry) our method can be used for
location recovery, that is the determination of relative pose up to a single
unknown scale. For this task, our method yields performance comparable to the
state-of-the-art with an order of magnitude speed-up. Our proposed numerical
framework is flexible in that it accommodates other approaches to location
recovery and can be used to speed up other methods. These properties are
demonstrated by extensively testing against state-of-the-art methods for
location recovery on 13 large, irregular collections of images of real scenes
in addition to simulated data with ground truth
The statistical laws of popularity: Universal properties of the box office dynamics of motion pictures
Are there general principles governing the process by which certain products
or ideas become popular relative to other (often qualitatively similar)
competitors? To investigate this question in detail, we have focused on the
popularity of movies as measured by their box-office income. We observe that
the log-normal distribution describes well the tail (corresponding to the most
successful movies) of the empirical distributions for the total income, the
income on the opening week, as well as, the weekly income per theater. This
observation suggests that popularity may be the outcome of a linear
multiplicative stochastic process. In addition, the distributions of the total
income and the opening income show a bimodal form, with the majority of movies
either performing very well or very poorly in theaters. We also observe that
the gross income per theater for a movie at any point during its lifetime is,
on average, inversely proportional to the period that has elapsed after its
release. We argue that (i) the log-normal nature of the tail, (ii) the bimodal
form of the overall gross income distribution, and (iii) the decay of gross
income per theater with time as a power law, constitute the fundamental set of
{\em stylized facts} (i.e., empirical "laws") that can be used to explain other
observations about movie popularity. We show that, in conjunction with an
assumption of a fixed lower cut-off for income per theater below which a movie
is withdrawn from a cinema, these laws can be used to derive a Weibull
distribution for the survival probability of movies which agrees with empirical
data. The connection to extreme-value distributions suggests that popularity
can be viewed as a process where a product becomes popular by avoiding failure
(i.e., being pulled out from circulation) for many successive time periods. We
suggest that these results may apply to popularity in general.Comment: 14 pages, 11 figure
Effects of Outdoor Exposure on Properties of I-Joists
Wood I-joists are often left uncovered and exposed to the weather during construction, allowing the oriented strandboard and laminated veneer lumber in these systems to be adversely affected by water absorption. Manufacturers typically specify that these materials be protected from wetting, but this can be difficult in wetter climates. There are few studies examining the potential effects of wetting on these building elements. In this study, flexural properties and ultimate tensile strength of I-joists exposed for extended periods of time during the rainy winter months in the Willamette Valley of western Oregon were evaluated. I-joists were removed from the field each month, dried, and then tested in static bending (flexure) using a six-point bending test. I-joist strength decreased as a function of exposure time and rainfall. Twenty-seven da of external exposure was associated with a significant increase in flexural variability. Further exposure was associated with significant decreases in I-joist strength (modulus of rupture). Although most I-joists never experience this degree of wetting, they can when construction is delayed. The results illustrate the detrimental effects of exposure to wetting during construction and support improved efforts to limit wetting
A Curious Truncation of N=4 Yang-Mills
The coupling constant dependence of correlation functions of BPS operators in
N=4 Yang-Mills can be expressed in terms of integrated correlation functions.
We approximate these integrated correlators by using a truncated OPE expansion.
This leads to differential equations for the coupling dependence. When applied
to a particular sixteen point correlator, the coupling dependence we find
agrees with the corresponding amplitude computed via the AdS/CFT
correspondence. We conjecture that this truncation becomes exact in the large N
and large 't Hooft coupling limit.Comment: 10 pages, LaTeX; additional comments, added reference
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