5,893 research outputs found
Microstructure-failure mode correlations in braided composites
Explication of the fracture processes of braided composites is needed for modeling their behavior. Described is a systematic exploration of the relationship between microstructure, loading mode, and micro-failure mechanisms in carbon/epoxy braided composites. The study involved compression and fracture toughness tests and optical and scanning electron fractography, including dynamic in-situ testing. Principal failure mechanisms of low sliding, buckling, and unstable crack growth are correlated to microstructural parameters and loading modes; these are used for defining those microstructural conditions which are strength limiting
Efficient dust ring formation in misaligned circumbinary discs
Binary systems exert a gravitational torque on misaligned discs orbiting them, causing differential precession which may produce disc warping and tearing. While this is well understood for gas-only discs, misaligned cirumbinary discs of gas and dust have not been thoroughly investigated. We perform SKI simulations of misaligned gas and dust discs around binaries to investigate the different evolution of these two components. We choose two different disc aspect ratios: A thin case for which the gas disc always breaks, and a thick one where a smooth warp develops throughout the disc. For each case, we run simulations of five different dust species with different degrees of coupling with the gas component, varying in Stokes number from. 0.002 (strongly coupled dust) to 1000 (effectively decoupled dust). We report two new phenomena: First, large dust grains in thick discs pile up at the warp location, forming narrow dust rings, due to a difference in precession between the gas and dust components. These pile ups do not form at gas pressure maxima, and hence are different.from conventional dust traps. This effect is most evident for St <^> 10-100. Secondly, thin discs tear and break only in the gas, while dust particles with St > 10 form a dense dust trap due to the steep pressure gradient caused by the break in the gas. We find that dust with St < 0.02 closely follow the gas particles, for both thin and thick discs, with radial drift becoming noticeable only for the largest grains in this range
A wideband circularly polarised cross-slot antenna with an L-shaped feed-line
This paper presents a new wideband and circularly polarised (CP) slot antenna realised by using an L-shaped feed underneath the cross-slot antenna, and tapered to the conventional microstrip feed-line. The proposed antenna is fabricated with an area of 75 × 80 mm2. The simulated results showed that the antenna had an impedance matching bandwidth of 34% from 1.3 to 1.83 GHz, and an axial ratio (AR) bandwidth of 20% from 1.36 to 1.66 GHz. A maximum gain value of 3.4 – 3.8 dBi has been achieved within the operating band. The proposed antenna is of a simple and single-substrate structure, suitable for the Global Navigation Satellite Systems (GNSS) application. The impedance bandwidth and radiation patterns have been confirmed by measurement
Superconducting Quantum Point contacts and Maxwell Potential
The quantization of the current in a superconducting quantum point contact is
reviewed and the critical current is discussed at different temperatures
depending on the carrier concentration as well by suggesting a constant
potential in the semiconductor and then a Maxwell potential. When the Fermi
wave length is comparable with the constriction width we showed that the
critical current has a step-like variation as a function of the constriction
width and the carrier concentration.Comment: 13 pages, 8 figures, some figures are clarified; scheduled to appear
in an issue in MPLB Vo.21, (2007
Bandwidth enhancement of circularly polarised slot global navigation satellite systems antenna using an integrated filter‐antenna approach
A technique to enhance the bandwidth of a circularly polarised antenna using the filter‐antenna design approach is presented. The design relies on adding a resonator coupled to the radiation element—an L‐shaped slot antenna in the case of global navigation satellite systems. This change in the feeding structure broadens both the impedance and the axial ratio (AR) bandwidths and allows more design flexibility. Compared with a reference L‐shaped slot antenna with a conventional feed, the proposed antenna design achieves a doubling of the impedance matching bandwidth from 19% to 41% over the frequency range from 1.2 to 1.81 GHz and a wider AR bandwidth from 35% to 44.5% in the range from 1.17 to 1.84 GHz. The AR bandwidth covers the entire impedance bandwidth. The effect of a metal reflector on antenna performance is also investigated and discussed
Capturing uncertainty in operation, behavior and weather in building performance assessment : an Egyptian case study.
New building energy standards have recently been proposed for Egypt. There is however insufficient data on the performance of existing buildings to provide a baseline for assessment of the impact of these new standards or other possible upgrade measures. In common with the rest of the world, there is also no standard design assessment method which takes account of the inherent uncertainty in operation, behavior, and weather. This paper first explores the current energy and environmental performance of offices in Egypt through a simple energy survey of multiple offices and more detailed investigation of an individual office building. The observed indoor thermal environment is compared against adaptive and non-adaptive thermal comfort standards. A method is then proposed for assessment of building performance which takes account of uncertainties in operation, behavior and weather through the definition and use of representative input parameter sets. The application of the method is illustrated for energy and thermal comfort performance of a typical Egyptian office building. The more general applicability of the method in design and policy, and potential for further developments, are discussed
Adaptive Processing of Spatial-Keyword Data Over a Distributed Streaming Cluster
The widespread use of GPS-enabled smartphones along with the popularity of
micro-blogging and social networking applications, e.g., Twitter and Facebook,
has resulted in the generation of huge streams of geo-tagged textual data. Many
applications require real-time processing of these streams. For example,
location-based e-coupon and ad-targeting systems enable advertisers to register
millions of ads to millions of users. The number of users is typically very
high and they are continuously moving, and the ads change frequently as well.
Hence sending the right ad to the matching users is very challenging. Existing
streaming systems are either centralized or are not spatial-keyword aware, and
cannot efficiently support the processing of rapidly arriving spatial-keyword
data streams. This paper presents Tornado, a distributed spatial-keyword stream
processing system. Tornado features routing units to fairly distribute the
workload, and furthermore, co-locate the data objects and the corresponding
queries at the same processing units. The routing units use the Augmented-Grid,
a novel structure that is equipped with an efficient search algorithm for
distributing the data objects and queries. Tornado uses evaluators to process
the data objects against the queries. The routing units minimize the redundant
communication by not sending data updates for processing when these updates do
not match any query. By applying dynamically evaluated cost formulae that
continuously represent the processing overhead at each evaluator, Tornado is
adaptive to changes in the workload. Extensive experimental evaluation using
spatio-textual range queries over real Twitter data indicates that Tornado
outperforms the non-spatio-textually aware approaches by up to two orders of
magnitude in terms of the overall system throughput
MHD simulations of disk-star interaction
We discuss a number of topics relevant to disk-magnetosphere interaction and
how numerical simulations illuminate them. The topics include: (1)
disk-magnetosphere interaction and the problem of disk-locking; (2) the wind
problem; (3) structure of the magnetospheric flow, hot spots at the star's
surface, and the inner disk region; (4) modeling of spectra from 3D funnel
streams; (5) accretion to a star with a complex magnetic field; (6) accretion
through 3D instabilities; (7) magnetospheric gap and survival of protoplanets.
Results of both 2D and 3D simulations are discussed.Comment: 12 pages, 10 figures, Star-Disk Interaction in Young Stars,
Proceedings of the International Astronomical Union, IAU Symposium, Volume
243. See animations at http://astro.cornell.edu/~romanova/projects.htm and at
http://astro.cornell.edu/us-rus
Minimal-memory realization of pearl-necklace encoders of general quantum convolutional codes
Quantum convolutional codes, like their classical counterparts, promise to
offer higher error correction performance than block codes of equivalent
encoding complexity, and are expected to find important applications in
reliable quantum communication where a continuous stream of qubits is
transmitted. Grassl and Roetteler devised an algorithm to encode a quantum
convolutional code with a "pearl-necklace encoder." Despite their theoretical
significance as a neat way of representing quantum convolutional codes, they
are not well-suited to practical realization. In fact, there is no
straightforward way to implement any given pearl-necklace structure. This paper
closes the gap between theoretical representation and practical implementation.
In our previous work, we presented an efficient algorithm for finding a
minimal-memory realization of a pearl-necklace encoder for
Calderbank-Shor-Steane (CSS) convolutional codes. This work extends our
previous work and presents an algorithm for turning a pearl-necklace encoder
for a general (non-CSS) quantum convolutional code into a realizable quantum
convolutional encoder. We show that a minimal-memory realization depends on the
commutativity relations between the gate strings in the pearl-necklace encoder.
We find a realization by means of a weighted graph which details the
non-commutative paths through the pearl-necklace. The weight of the longest
path in this graph is equal to the minimal amount of memory needed to implement
the encoder. The algorithm has a polynomial-time complexity in the number of
gate strings in the pearl-necklace encoder.Comment: 16 pages, 5 figures; extends paper arXiv:1004.5179v
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