5,396 research outputs found
Coping with Poorly Understood Domains: the Example of Internet Trust
The notion of trust, as required for secure operations over the Internet, is important for ascertaining the source of received messages. How can we measure the degree of trust in authenticating the source? Knowledge in the domain is not established, so knowledge engineering becomes knowledge generation rather than mere acquisition. Special techniques are required, and special features of KBS software become more important than in conventional domains. This paper generalizes from experience with Internet trust to discuss some techniques and software features that are important for poorly understood domains
Mariner Mars 1969: Atmospheric results
Results of investigation of probable atmospheric effects appearing in Mariner '69 TV pictures that have undergone noise removal and preliminary decalibration are described. Two distinct types of haze are distinguished: north polar haze, seen prominently against the face of the planet in blue photographs, and thin haze, usually identified by its appearance on the limb and not strongly colored. Thin haze is surprisingly widespread, particularly in the southern hemisphere. Discrete bright features, which may be evidence for condensation on the ground or in the atmosphere, are described. These occur where bright features have often been seen from earth, in a region where very large multiple-ringed structures seem to dominate the surface morphology. The speculation that these may be evidence for local water-vapor exchange between ground and atmosphere is raised, and some constraints on local subsurface water-vapor sources in the Mars tropics are described. Finally, some implications of the Mariner '69 results for atmospheric exploration by Mariner '71 are briefly discussed
Motor Output Structure in Targeted Aiming: A Mechanistic Model
Studies using a variety of experimental tasks have established that when humans repeatedly produce an action, fluctuations in action output are highest at the lowest frequencies and fluctuation magnitude (power) systematically declines as frequency increases. Such time series structure is termed pink noise. However, the appearance of pink noise seems to be limited to tasks where action is executed in the absence of task-related feedback. A few studies have demonstrated that when action was executed in the presence of task-related feedback, power was evenly distributed across all spectral frequencies—i.e., white noise was revealed. Here, participants produced cyclical aiming movements under visual feedback conditions and we sought to determine whether variations of both the movement amplitude requirement (A) and the target width (W)—in the form of the index of difficulty [ID = log2(2A/W)]—would predict the structure of movement amplitude (MA) time series. There were five ID levels, and there was a small-, medium-, and large-scale version of each ID: The A and W values doubled with each increment in scale level. Given that increases in ID are known to induce increased reliance on the available visual feedback, we predicted an ID-induced shift in MA time series structure from pink to white noise, with no change in MA structure across scale levels.https://engagedscholarship.csuohio.edu/u_poster_2014/1020/thumbnail.jp
Proposal for a loophole-free Bell test based on spin-photon interactions in cavities
We present a scheme to demonstrate loophole-free Bell inequality violation
where the entanglement between photon pairs is transferred to solid state
(spin) qubits mediated by cavity QED interactions. As this transfer can be
achieved in a heralded way, our scheme is basically insensitive to losses on
the channel. This makes it appealing for the implementation of quantum
information protocols based on nonlocality, such as device-independent quantum
key distribution. We consider potential experimental realisations of our scheme
using single atom, colour centre and quantum dot cavity systems.Comment: 7 pages, 4 figure
First principles calculations of the Shift Current Bulk Photovoltaic Effect in Ferroelectrics
We calculate the bulk photovoltaic response of the ferroelectrics BaTiO
and PbTiO from first principles by applying "shift current" theory to the
electronic structure from density functional theory. The first principles
results for BaTiO reproduce eperimental photocurrent direction and
magnitude as a function of light frequency, as well as the dependence of
current on light polarization, demonstrating that shift current is the dominant
mechanism of the bulk photovoltaic effect in BaTiO. Additionally, we
analyze the relationship between response and material properties in detail.
The photocurrent does not depend simply or strongly on the magnitude of
material polarization, as has been previously assumed; instead, electronic
states with delocalized, covalent bonding that is highly asymmetric along the
current direction are required for strong shift current enhancements. The
complexity of the response dependence on both external and material parameters
suggests applications not only in solar energy conversion, but to
photocatalysis and sensor and switch type devices as well.Comment: First submitted April 2011, submitted PRL July 201
Chromosome Abnormalities and Repeated Abortion: A Preliminary Report
In view of the increased frequency of chromosome rearrangements demonstrated in these couples and the importance of counseling for future pregnancies, it would be wise to consider cytogenetic evaluation when all other probable causes for recurrent abortion have been ruled out
Stability of polarization singularities in disordered photonic crystal waveguides
The effects of short-range disorder on the polarization characteristics of light in photonic crystal waveguides were investigated using finite-difference time-domain simulations with a view to investigating the stability of polarization singularities. It was found that points of local circular polarization (C points) and contours of linear polarization (L lines) continued to appear even in the presence of high levels of disorder, and that they remained close to their positions in the ordered crystal. These results are a promising indication that devices exploiting polarization in these structures are viable given current fabrication standards
The roles of segmental and tandem gene duplication in the evolution of large gene families in Arabidopsis thaliana
BACKGROUND: Most genes in Arabidopsis thaliana are members of gene families. How do the members of gene families arise, and how are gene family copy numbers maintained? Some gene families may evolve primarily through tandem duplication and high rates of birth and death in clusters, and others through infrequent polyploidy or large-scale segmental duplications and subsequent losses. RESULTS: Our approach to understanding the mechanisms of gene family evolution was to construct phylogenies for 50 large gene families in Arabidopsis thaliana, identify large internal segmental duplications in Arabidopsis, map gene duplications onto the segmental duplications, and use this information to identify which nodes in each phylogeny arose due to segmental or tandem duplication. Examples of six gene families exemplifying characteristic modes are described. Distributions of gene family sizes and patterns of duplication by genomic distance are also described in order to characterize patterns of local duplication and copy number for large gene families. Both gene family size and duplication by distance closely follow power-law distributions. CONCLUSIONS: Combining information about genomic segmental duplications, gene family phylogenies, and gene positions provides a method to evaluate contributions of tandem duplication and segmental genome duplication in the generation and maintenance of gene families. These differences appear to correspond meaningfully to differences in functional roles of the members of the gene families
Sub-nanosecond signal propagation in anisotropy engineered nanomagnetic logic chains
Energy efficient nanomagnetic logic (NML) computing architectures propagate
and process binary information by relying on dipolar field coupling to reorient
closely-spaced nanoscale magnets. Signal propagation in nanomagnet chains of
various sizes, shapes, and magnetic orientations has been previously
characterized by static magnetic imaging experiments with low-speed adiabatic
operation; however the mechanisms which determine the final state and their
reproducibility over millions of cycles in high-speed operation (sub-ns time
scale) have yet to be experimentally investigated. Monitoring NML operation at
its ultimate intrinsic speed reveals features undetectable by conventional
static imaging including individual nanomagnetic switching events and
systematic error nucleation during signal propagation. Here, we present a new
study of NML operation in a high speed regime at fast repetition rates. We
perform direct imaging of digital signal propagation in permalloy nanomagnet
chains with varying degrees of shape-engineered biaxial anisotropy using
full-field magnetic soft x-ray transmission microscopy after applying single
nanosecond magnetic field pulses. Further, we use time-resolved magnetic
photo-emission electron microscopy to evaluate the sub-nanosecond dipolar
coupling signal propagation dynamics in optimized chains with 100 ps time
resolution as they are cycled with nanosecond field pulses at a rate of 3 MHz.
An intrinsic switching time of 100 ps per magnet is observed. These
experiments, and accompanying macro-spin and micromagnetic simulations, reveal
the underlying physics of NML architectures repetitively operated on nanosecond
timescales and identify relevant engineering parameters to optimize performance
and reliability.Comment: Main article (22 pages, 4 figures), Supplementary info (11 pages, 5
sections
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